Method for monitoring cement using polymer-based capsules

ABSTRACT

Embodiments provide a method for monitoring structural integrity of a hardened cement. An aramide capsule, a cement, and a water to form a cement slurry. The cement slurry is set to form a hardened cement, where the aramide capsule is embedded in the hardened cement. Imperfections of the hardened cement are detected by measuring electrical resistivity of the hardened cement. The aramide capsule is formed by interfacial polymerization using a surfactant, a dispersed monomer, a crosslinker such that a semi-permeable membrane is formed surrounding a core.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application of U.S. patent application Ser. No. 16/018,336 filed Jun. 26, 2018, now issued as U.S. Pat. No. 10,669,469, which is a continuation application of U.S. patent application Ser. No. 15/701,670 filed Sep. 12, 2017, now issued as U.S. Pat. No. 10,377,940, which claims priority from U.S. Provisional Application Ser. No. 62/397,126 filed Sep. 20, 2016; this application is a continuation-in-part application of U.S. patent application Ser. No. 16/230,391 filed Dec. 21, 2018, now issued as U.S. Pat. No. 10,619,085, which claims priority from U.S. Provisional Patent Application No. 62/612,754 filed Jan. 2, 2018; all of the above-referenced applications are incorporated by reference in their entireties into this application.

BACKGROUND 1. Technical Field

The present disclosure relates to a cement, and method of making the cement, that bonds casing to a wellbore. More specifically, the present disclosure relates to a cement, and method of making the cement, that bonds casing to a wellbore, and that includes cross-linked polymers. In addition, the present disclosure relates to monitoring cement. More specifically, the present disclosure relates to a method of monitoring the structural integrity of cement by embedding polymer-based hollow capsules in the cement.

2. Related Art

Hydrocarbons that are produced from subterranean formations typically flow from the formations to surface via wellbores drilled from surface that intersect the formations. Most wellbores are lined with casing and strings of production tubing inserted within the casing that are for conveying the hydrocarbons to surface. The casing is usually bonded to the inner surface of the wellbore with a cement that is injected into an annulus that is between the casing and wellbore. In addition to anchoring the casing within the wellbore, the cement also isolates adjacent zones within the formation from one another. Without the cement isolating these adjacent zones fluids from the different zones, which are sometimes different, could become mixed in the annular space between the casing and wellbore wall. When one of the different fluids is water, separating it from the hydrocarbon is required. Further, if the water producing zone is at a pressure exceeding that of a hydrocarbon producing zone, water sometimes migrates into the hydrocarbon producing zone to thereby reduce the hydrocarbon producing potential of the wellbore.

The cement also prevents hydrocarbon fluid from flowing uphole from a hydrocarbon producing zone to the surface and in the annulus between the casing and the wellbore wall. Without the cement, or in instances when cement has failed, hydrocarbons are known to migrate to surface and then present a safety hazard to operations personnel. One problematic area for gas migration exists for deep wells, where fluid densities often as high as 22 pounds per gallon are used to control gas or formation fluid influx. To control gas migration, cement densities for successfully cementing of the zone of interest are sometimes as high as 22.7 pounds per gallon. As a cement slurry sets, hydrostatic pressure is reduced on the formation. During this transition, reservoir gases can travel up through the cement column resulting in gas being present at the surface. The permeable channels from which the gas flows cause operational and safety problems at the well site. Causes of gas channeling include: (1) bad mud/spacer/cement design that allows passage of water and gas resulting in failures in cementing operations; (2) high fluid loss from cement slurries, which causes water accumulation and results in micro-fractures within the cement body; and (3) cements not providing sufficient hydrostatic pressure to control the high pressure formation.

In many wellbores, cement can be used to form a layer between a casing and the formation. Delivery of additives to the cement can be problematic for a variety of reasons. First, the additives must be mixed with the cement slurry and delivered along with the slurry to the downhole location. Second, the additives must survive intact at the extreme downhole conditions in order to impart their additive properties. Third, controlling the release rate of an additive can be difficult in a downhole environment.

Encapsulation-based systems are of interest in the oil and gas industry in applications such as chemical additive preservation, small molecule release, particle delivery, and self-sealing materials. Many methods are used to encapsulate relevant chemical additives for the controlled release of contents. Example capsulation materials include polymeric coatings, inorganic shells, and mesoporous materials.

When placing cement in a wellbore, a multitude of additives (usually in large quantities) are considered and added to the slurry in order to meet a variety of functional needs suitable for diverse wellbore conditions. However, using large quantities of certain additives (for example, retarders and fluid loss control agents) may destabilize the slurry at the surface even before introducing the slurry into the wellbore.

SUMMARY

Disclosed are compositions and methods for use in cement slurries. Specifically, disclosed are compositions and methods for controlling a downhole environment during cement operations.

Embodiments of the disclosure provide an example of a cement composition for use in a wellbore and that includes a cement, a calcium silicate in the cement, and an aramide compound that is formed from a trifunctional carboxylic acid and an organic compound comprising nitrogen. Examples exist where the diamine is one of ethylenediamine, 1,3-diaminobenzene, 1,4-diaminobenzene, 1,6-diaminohexane, 1,4-phenylenediamine, or combinations. In one example, the 1,6-diaminohexane is mixed with sebacoyl chloride. In one example, the organic compound having nitrogen includes a diamine. Optionally the aramide is one or more of poly(ethylene trimesoylamide), poly-(meta-phenylene trimesoylamide), poly-(para-phenylene trimesoylamide), poly(hexamethylene trimesoylamide), poly(hexamethylene-co-sebacoyl trimesoylamide), poly-(para-phenylene trimesoylamide), and a blend of poly-(meta-phenylene trimesoylamide) and poly(hexamethylene trimesoylamide). In one embodiment, the aramide compound is a aramide condensate compound. In an alternative, the aramide compound is cross-linked.

Embodiments of the disclosure also provide an example of a cement composition for use in a wellbore is disclosed and that includes a cement and an amide compound that is formed from an aromatic triacid chloride and an organic compound having nitrogen. An example exists where a polyamide compound is included with the amide compound. A silica, such as crystalline silica or calcium silicate, is optionally included with the cement composition. In one alternative, the amine is a diamine, such as ethylenediamine, 1,3-diaminobenzene, 1,4-diaminobenzene, 1,6-diaminohexane, 1,4-phenylenediamine, and combinations. The triacid chloride can be 1,3,5-benzenetricarboxylic acid chloride. Optionally, the organic compound having nitrogen is an amine. The amide compound is alternatively cross-linked.

Embodiments of the disclosure also provide a method of forming a cement composition for use in a wellbore, and which includes forming an amide by combining a trifunctional carboxylic acid with an organic compound having nitrogen, combining an amount of cement, water, and the amide to form a mixture, and curing the mixture to form a cement composition. In one example the amide is a cross-linked polyamide. The polyamide can be an aramide having a molecular weight that ranges from about 189 Daltons to about 555 Daltons. The organic compound that having nitrogen optionally includes diamine. In one example, the diamine is one of ethylenediamine, 1,3-diaminobenzene, 1,4-diaminobenzene, 1,6-diaminohexane, 1,4-phenylenediamine, and combinations, and is mixed with sebacoyl chloride. Curing the cement can advantageously occur inside of a wellbore.

Embodiments of the disclosure also provide a system for the controlled release of encapsulated cargo that utilizes engineered features of permeable polymeric shell walls. Using vesicles or capsules, cement additives can be delivered without physical or chemical modification. Various cement formulations can be designed utilizing numerous combinations of vesicles with various encapsulants. Vesicle systems are particularly useful for delivering agents such as chemical additives and small molecules to provide beneficial interactions in cement slurry applications. Such cement slurry applications include chemical delivery and controlled release of chemical additives during placement of a slurry downhole.

In one aspect, a method for encapsulating a cement additive for use in a wellbore includes the step of mixing a continuous solvent and a surfactant to produce a continuous phase. The method includes the step of mixing a dispersed solvent, a dispersed monomer, and the cement additive to produce a dispersed phase. The dispersed solvent and the continuous solvent are immiscible. The method includes the step of mixing the continuous phase and the dispersed phase to form a mixture having an emulsion such that the dispersed phase is dispersed as droplets in the continuous phase. An interface defines the droplets of the dispersed phase dispersed in the continuous phase. The method includes the step of adding a crosslinker to the mixture. The method includes the step of allowing an aramide polymer to form on the interface of the droplets, such that the aramide polymer forms a semi-permeable membrane around a core. The core contains the dispersed phase, such that the semi-permeable membrane around the core forms the aramide capsule. The method includes the step of allowing the aramide capsule to settle from the mixture. The method includes the step of separating the aramide capsule from the mixture using a separation method.

In certain aspects, the dispersed solvent can include water, ethanol, and methanol. In certain aspects, the dispersed monomer includes an amine group. In certain aspects, the dispersed monomer can include ethylenediamine, meta-phenylenediamine, para-phenylenediamine, and hexamethylenediamine. In certain aspects, the continuous solvent can include oil, mineral oil, cyclohexane, and chloroform. In certain aspects, the crosslinker can include 1,3,5-benzenetricarbonyl trichloride and sebacoyl chloride. In certain aspects, the cement additive is water-soluble and can include sealing reagents, anti-gas migration additives, high-temperature retarders, fluid-loss additives, accelerators, and superplasticizers.

In one aspect, a method for controlled release of a cement additive for use in a wellbore includes the step of mixing an aramide capsule with a cement slurry to form an additive-containing slurry. The method includes the step of introducing the additive-containing slurry into the wellbore. The aramide capsule is formed by the step of mixing a continuous solvent and a surfactant to produce a continuous phase. The aramide capsule is formed by the step of mixing a dispersed solvent, a dispersed monomer, and the cement additive to produce a dispersed phase. The dispersed solvent and the continuous solvent are immiscible. The aramide capsule is formed by the step of mixing the continuous phase and the dispersed phase to form a mixture having an emulsion such that the dispersed phase is dispersed as droplets in the continuous phase. An interface defines the droplets of the dispersed phase dispersed in the continuous phase. The aramide capsule is formed by the step of adding a crosslinker to the mixture. The aramide capsule is formed by the step of allowing an aramide polymer to form on the interface of the droplets, such that the aramide polymer forms a semi-permeable membrane around a core. The core contains the dispersed phase, such that the semi-permeable membrane around the core forms the aramide capsule. The aramide capsule is formed by the step of allowing the aramide capsule to settle from the mixture. The aramide capsule is formed by the step of separating the aramide capsule from the mixture using a separation method.

In certain aspects, the method further includes the step of allowing the cement additive to permeate from the core through the semi-permeable membrane to the cement slurry. The method further includes the step of allowing the cement additive to have a beneficial interaction with the cement slurry. In certain aspects, the method further includes the step of allowing the additive-containing slurry to set to form a hardened cement. The aramide capsule is embedded in the hardened cement. The method further includes the step of allowing the cement additive to permeate from the core through the semi-permeable membrane to the hardened cement. The method further includes the step of allowing the cement additive to have a beneficial interaction with the hardened cement. In certain aspects, the hardened cement has an unconfined compression strength ranging from about 3,000 pounds per square inch (psi) to about 3,400 psi. In certain aspects, the method further includes the step of allowing the additive-containing slurry to set to form a hardened cement. The aramide capsule is embedded in the hardened cement. The method further includes the step of allowing the semi-permeable membrane to burst such that the cement additive is released from the aramide capsule and migrates through the hardened cement. The method further includes the step of allowing the cement additive to have a beneficial interaction with the hardened cement. In certain aspects, the hardened cement has an unconfined compression strength ranging from about 3,000 psi to about 3,400 psi.

In certain aspects, the dispersed solvent can include water, ethanol, and methanol. In certain aspects, the dispersed monomer includes an amine group. In certain aspects, the dispersed monomer can include ethylenediamine, meta-phenylenediamine, para-phenylenediamine, and hexamethylenediamine. In certain aspects, the continuous solvent can include oil, mineral oil, cyclohexane, and chloroform. In certain aspects, the crosslinker can include 1,3,5-benzenetricarbonyl trichloride and sebacoyl chloride. In certain aspects, the cement additive is water-soluble and can include sealing reagents, anti-gas migration additives, high-temperature retarders, fluid-loss additives, accelerators, and superplasticizers. In certain aspects, the aramide polymer of the aramide capsule is present in the additive-containing slurry at a concentration of at least about 3% by weight of cement. In certain aspects, the cement additive is tethered in the core of the aramide capsule via site-isolation of a water-soluble polymer.

In one aspect, an aramide capsule for use in a cement environment includes a semi-permeable membrane including an aramide polymer. The semi-permeable membrane forms a shell with a core, such that the core contains a cement additive. The semi-permeable membrane is operable to allow the cement additive to permeate from the core through the semi-permeable membrane to the cement environment. The aramide capsule includes the cement additive. The cement additive is operable to impart a beneficial interaction on the cement environment. The aramide polymer includes subunits derived from a monomer including a di-functional amino group and subunits derived from a crosslinker including an acyl chloride.

In certain aspects, the aramid capsule further includes a linear polymer. The linear polymer is water-soluble and is operable to tether the cement additive in the core via site-isolation. In certain aspects, the linear polymer can include polyethylene glycols, polystyrenes, polyethylene imine, polyvinyl alcohols, and polyvinylpyrrolidone. In certain aspects, the monomer can include ethylenediamine, meta-phenylenediamine, para-phenylenediamine, and hexamethylenediamine. In certain aspects, the crosslinker can include 1,3,5-benzenetricarbonyl trichloride and sebacoyl chloride. In certain aspects, the cement additive is water-soluble and can include sealing reagents, anti-gas migration additives, high-temperature retarders, fluid-loss additives, accelerators, and superplasticizers.

Embodiments of the disclosure provide a method for monitoring structural integrity of a hardened cement. The method includes the step of mixing an aramide capsule, a cement, and a water to form a cement slurry. The aramide capsule is formed by the step of mixing a continuous solvent and a surfactant to produce a continuous phase. The aramide capsule is formed by the step of mixing a dispersed solvent and a dispersed monomer to produce a dispersed phase. The dispersed solvent and the continuous solvent are immiscible. The aramide capsule is formed by the step of mixing the continuous phase and the dispersed phase to form a mixture having an emulsion such that the dispersed phase is dispersed as droplets in the continuous phase. An interface defines the droplets of the dispersed phase dispersed in the continuous phase. The aramide capsule is formed by the step of adding a crosslinker to the mixture. The aramide capsule is formed by the step of allowing an aramide polymer to form on the interface of the droplets, such that the aramide polymer forms a semi-permeable membrane around a core. The core contains the dispersed phase, such that the semi-permeable membrane around the core forms the aramide capsule. The aramide capsule is formed by the step of allowing the aramide capsule to settle from the mixture. The aramide capsule is formed by the step of separating the aramide capsule from the mixture using a separation method. The aramide capsule is formed by the step of drying the aramide capsule such that the core is hollow. The aramide capsule exists as a free flowing powder. The method includes the step of allowing the cement slurry to set to form the hardened cement. The aramide capsule is embedded in the hardened cement. The method includes the step of detecting imperfections of the hardened cement by measuring electrical resistivity of the hardened cement.

In some embodiments, the cement slurry has a water-to-cement mass ratio ranging between 0.1 and 0.8. In some embodiments, the aramide polymer of the aramide capsule is present in the cement slurry at a concentration ranging between 0.5% and 5% by weight of the cement. In some embodiments, the aramide capsule has a diameter ranging between 500 and 1,200 microns. In some embodiments, the aramide capsule has a diameter ranging between 10 and 500 microns. In some embodiments, the aramide capsule has a wall thickness ranging between 3 and 5 microns. In some embodiments, the dispersed solvent includes water, ethanol, methanol, and combinations of the same. In some embodiments, the dispersed monomer includes polyethylenimine, 1,4-diaminobenzene, 1,3-diaminobenzene, 1,6-diaminohexane, and combinations of the same. In some embodiments, the continuous solvent includes cyclohexane, chloroform, and combinations of the same. In some embodiments, the crosslinker is 1,3,5-benzenetricarbonyl trichloride.

Embodiments of the disclosure also provide a method for monitoring structural integrity of a cemented wellbore. The method includes the step of mixing an aramide capsule, a cement, and a water to form a cement slurry. The aramide capsule is formed by the step of mixing a continuous solvent and a surfactant to produce a continuous phase. The aramide capsule is formed by the step of mixing a dispersed solvent and a dispersed monomer to produce a dispersed phase. The dispersed solvent and the continuous solvent are immiscible. The aramide capsule is formed by the step of mixing the continuous phase and the dispersed phase to form a mixture having an emulsion such that the dispersed phase is dispersed as droplets in the continuous phase. An interface defines the droplets of the dispersed phase dispersed in the continuous phase. The aramide capsule is formed by the step of adding a crosslinker to the mixture. The aramide capsule is formed by the step of allowing an aramide polymer to form on the interface of the droplets, such that the aramide polymer forms a semi-permeable membrane around a core. The core contains the dispersed phase, such that the semi-permeable membrane around the core forms the aramide capsule. The aramide capsule is formed by the step of allowing the aramide capsule to settle from the mixture. The aramide capsule is formed by the step of separating the aramide capsule from the mixture using a separation method. The aramide capsule is formed by the step of drying the aramide capsule such that the core is hollow. The aramide capsule exists as a free flowing powder. The method includes the step of injecting the cement slurry into a drilled wellbore. The method includes the step of allowing the cement slurry to set to form the cemented wellbore. The aramide capsule is embedded in the hardened cement. The method includes the step of detecting imperfections of the cemented wellbore by measuring electrical resistivity of the cemented wellbore.

In some embodiments, the cement slurry has a water-to-cement mass ratio ranging between 0.1 and 0.8. In some embodiments, the aramide polymer of the aramide capsule is present in the cement slurry at a concentration ranging between 0.5% and 5% by weight of the cement. In some embodiments, the aramide capsule has a diameter ranging between 500 and 1,200 microns. In some embodiments, the aramide capsule has a diameter ranging between 10 and 500 microns. In some embodiments, the aramide capsule has a wall thickness ranging between 3 and 5 microns. In some embodiments, the dispersed solvent includes water, ethanol, methanol, and combinations of the same. In some embodiments, the dispersed monomer includes polyethylenimine, 1,4-diaminobenzene, 1,3-diaminobenzene, 1,6-diaminohexane, and combinations of the same. In some embodiments, the continuous solvent includes cyclohexane, chloroform, and combinations of the same. In some embodiments, the crosslinker is 1,3,5-benzenetricarbonyl trichloride.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the scope will become better understood with regard to the following descriptions, claims, and accompanying drawings. It is to be noted, however, that the drawings illustrate only several embodiments and are therefore not to be considered limiting of the scope as it can admit to other equally effective embodiments.

FIG. 1 is a graphical representation showing weight loss percent versus temperature of a cross linked polyamide as disclosed here.

FIG. 2 is a graphical representation showing plots reflecting compressive loads applied to cement samples versus time.

FIGS. 3A-3C are perspective views of the cement samples loaded to obtain the data presented in FIG. 2.

FIG. 4 is a graphical representation showing plots of compression strength of cement samples versus a loading rate.

FIGS. 5A-5E are graphical illustrations of stress-strain data obtained by repeated loading of cement samples.

FIGS. 6A and 6B are graphical depictions respectively of compression strength and Young's modulus measured over time and at varying temperature of different cements.

FIG. 7 is a side partial sectional view of an example of a wellbore having cement made in accordance with the present disclosure.

FIG. 8 is a photographic representation of the aramide capsules embedded in a cement slurry, as imaged by optical microscopy at ambient conditions.

FIG. 9 is a graphical representation showing ultraviolet/visible (UV/Vis) absorbance of the encapsulant released from the aramide capsule samples over time.

FIG. 10 is a photographic representation of the aramide capsule, as imaged by optical microscopy at ambient conditions.

FIG. 11 is a graphical representation showing viscosity of the cement slurry having the encapsulant within the aramide capsule samples of varying monomer concentration.

FIG. 12 is a graphical representation showing viscosity of the cement slurry having aramide capsule samples over time.

FIG. 13 is a graphical representation showing unconfined compression strengths of cement samples.

FIG. 14 is a graphical representation showing a time-dependent increase in yield of aramide capsules.

FIG. 15A is a schematic representation of the chemical structure an aramide capsule.

FIGS. 15B and 15C are photographic representations of the aramide capsules, as imaged by optical microscopy at ambient conditions. FIG. 15D is a photographic representation of the aramid capsule, as imaged by fluorescence microscopy.

FIG. 16A is a schematic representation of the chemical structure an aramide capsule.

FIGS. 16B and 16C are photographic representations of the aramide capsules, as imaged by optical microscopy at ambient conditions.

FIG. 17 is a graphical representation showing electrical resistivity of cement samples with or without the aramide capsules.

In the accompanying Figures, similar components or features, or both, may have a similar reference label.

DETAILED DESCRIPTION

The disclosure refers to particular features, including process or method steps and systems. Those of skill in the art understand that the disclosure is not limited to or by the description of embodiments given in the specification. The subject matter of this disclosure is not restricted except only in the spirit of the specification and appended claims.

Those of skill in the art also understand that the terminology used for describing particular embodiments does not limit the scope or breadth of the embodiments of the disclosure. In interpreting the specification and appended claims, all terms should be interpreted in the broadest possible manner consistent with the context of each term. All technical and scientific terms used in the specification and appended claims have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs unless defined otherwise.

Although the disclosure has been described with respect to certain features, it should be understood that the features and embodiments of the features can be combined with other features and embodiments of those features.

Although the disclosure has been described in detail, it should be understood that various changes, substitutions, and alternations can be made without departing from the principle and scope of the disclosure. Accordingly, the scope of the present disclosure should be determined by the following claims and their appropriate legal equivalents.

As used throughout the disclosure, the singular forms “a,” “an,” and “the” include plural references unless the context clearly indicates otherwise.

As used throughout the disclosure, the word “about” includes +/−5% of the cited magnitude. The word “substantially” includes +/−5% of the cited magnitude.

As used throughout the disclosure, the words “comprise,” “has,” “includes,” and all other grammatical variations are each intended to have an open, non-limiting meaning that does not exclude additional elements, components or steps. Embodiments of the present disclosure may suitably “comprise,” “consist,” or “consist essentially of” the limiting features disclosed, and may be practiced in the absence of a limiting feature not disclosed. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

As used throughout the disclosure, the words “optional” or “optionally” means that the subsequently described event or circumstances can or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

Where a range of values is provided in the specification or in the appended claims, it is understood that the interval encompasses each intervening value between the upper limit and the lower limit as well as the upper limit and the lower limit. The disclosure encompasses and bounds smaller ranges of the interval subject to any specific exclusion provided.

Where reference is made in the specification and appended claims to a method comprising two or more defined steps, the defined steps can be carried out in any order or simultaneously except where the context excludes that possibility.

As used throughout the disclosure, terms such as “first” and “second” are arbitrarily assigned and are merely intended to differentiate between two or more components of an apparatus. It is to be understood that the words “first” and “second” serve no other purpose and are not part of the name or description of the component, nor do they necessarily define a relative location or position of the component. Furthermore, it is to be understood that that the mere use of the term “first” and “second” does not require that there be any “third” component, although that possibility is contemplated under the scope of the present disclosure.

As used throughout the disclosure, spatial terms described the relative position of an object or a group of objects relative to another object or group of objects. The spatial relationships apply along vertical and horizontal axes. Orientation and relational words are for descriptive convenience and are not limiting unless otherwise indicated.

Embodiments of the disclosure provide an example of a cement composition that is used in a wellbore for bonding a tubular to sidewalls of the wellbore; and that blocks axial flow in an annulus between the tubular and the wellbore sidewalls. Blocking flow through the annulus isolates vertically spaced apart portions of the formation from one another. In an embodiment, the cement composition includes a polymer. An example of the composition having the polymer experienced a 25% increase in compressive strength over that of compositions having latex.

In an example embodiment, the cement composition includes a mixture of cement, water, and polymer. An optional anti-foaming agent can be included in the mixture. In an embodiment where the cement is a Portland cement, the cement includes tri-calcium silicate (C₃S) and di-calcium silicate (C₂S). When mixed with water, both C₃S and C₂S can hydrate to form calcium silicate hydrate (C—S—H) gel. Further, in one example embodiment, the polymer is a cross-linked polymer. In another example embodiment, the polymer is a polyamide, and can be a cross-linked polyamide. Yet further optionally, the polymer is an aramide; examples exist where the aramide is a cross-linked aramide. In one embodiment the polyamide is formed by a condensation reaction. In an optional example, the condensation reaction is between monomers. Examples exist where the polyamide is aliphatic, and examples exist where the polyamide is aromatic. In an example, the polymer was produced using a monomer that mimics the flexibility of a nylon using a long carbon-chain monomer, and the rigidity and strength of an aramide using an aromatic monomer. In an alternative, the polymer is synthesized by reacting a trifunctional monomer with a bifunctional monomer. In an embodiment, the polymer, the polyamide, or the aramide products are linear, branched, or networked. Alternatives exist where the polymer, the polyamide, or the aramide condensates are formed using a trifunctional monomer, which for the purposes of discussion here is referred to as a crosslinker; accordingly, such formed products are correspondingly referred to as being crosslinked.

Embodiments of the disclosure provide compositions and methods directed to cement additive delivery systems. Advantageously, the composition and methods described here can mitigate gas migration and the formation of micro-annuli in cement slurries. Advantageously, the compositions and methods can increase the compression strength following the thickening time, decreasing the permeability of the hardened cement. Advantageously, the compositions and methods described can provide high-temperature cement additives that enable the delivery of cement additives at controlled release after a cement slurry has been placed in a wellbore.

Chemical additives are frequently used for designing cement slurry formulations to produce reliable cement sheaths for well construction. However, the chemical additives may not properly function at wellbore conditions where the extreme temperature and pressure may alter the desired chemical functionalities of the additives. Advantageously, the chemical additives (for example, a dispersant or an accelerator) can be encapsulated by methods incorporating interfacial polymerization, such that the chemical additives are placed within a hollow polymer shell and shielded from extreme wellbore conditions. The shells are designed for the delayed release of the chemical additives providing molecular and temporal control for field applications. Similar to chemical additives, interfacial polymerization can be employed for encapsulating engineered additives. The engineered additives can also be placed within the hollow polymer shell for the controlled release of the additives in the wellbore.

As used throughout, “capsule” refers to one or more particles of particular combination of semi-permeable membrane and cement additive. A reference to the singular capsule includes multiple particles. A reference to the plural capsules is a reference to compositions of different semi-permeable membranes.

As used throughout, “shell” refers to an enclosure that completely surrounds a core.

As used throughout, “semi-permeable” means that certain components are able to pass through. The ability for a component to pass through a semi-permeable membrane depends on the size and charge of the component.

As used throughout, “shearing rate” refers to the mixing speed when forming the emulsion-based capsules.

As used throughout, “beneficial interaction” means the cement additive imparts a benefit to the cement slurry or hardened cement or the properties of the cement slurry or hardened slurry. “Benefit” as used here means a positive impact. Non-limiting examples of beneficial interactions include sealing the cement to mitigate micro-annuli formation of set cements during the lifetime of the well and releasing cement additives in a controlled fashion as the slurry is mixed with the additives or as the mixed slurry is introduced downhole. Non-limiting examples of beneficial interactions also include gas migration control and enhancing mechanical properties of set cement.

As used throughout, “cement environment” refers collectively any stage of the cement process and includes both the cement slurry and the hardened cement.

As used throughout, “immiscible” means not forming a homogeneous mixture when two or more solvents are added together. Immiscible solvents may form an emulsion. Non-limiting examples of immiscible solvents include oil and water, and cyclohexane and water.

As used throughout, “wellbore” refers to a hole drilled into a subsurface formation of the earth, where the subsurface formation can contain hydrocarbons. The wellbore can have a depth from the surface and a diameter and can transverse the subsurface formation vertically, horizontally at a parallel to the surface, or at any angle between vertically and parallel.

As used throughout, “aramide” refers to an aromatic polyamide. Terms such as “aramids,” “aramides,” “polyaramids,” “polyaramides,” “aramid polymers,” “aramide polymers,” and “aromatic polyamides” are used interchangeably. Commercial examples of aramides include para-aramides such as Kevlar® (available from DuPont®, Wilmington, Del.), Technora® (available from Teijin Aramid USA, Inc, Conyers, Ga.), Twaron® (available from Teijin Aramid USA, Inc, Conyers, Ga.), and Heracron® (available from Kolon Industries, Inc., Gwachon, Korea), and meta-aramides such as Nomex® (available from DuPont®, Wilmington, Del.) and Teijinconex® (available from Teijin Aramid USA, Inc, Conyers, Ga.). A para-aramide is an aramide where the polymer chain is connected via the para positions of an acyl group subunit or functional group. A meta-aramide is an aramide where the polymer chain is connected via the meta positions of an acyl group subunit or functional group.

The aramide capsule can be composed of a cement additive encapsulated by a semi-permeable membrane. The aramide capsule can have a specific gravity of between 1.0 and 1.5, alternately of between 1.2 and 1.4. The specific gravity of the aramide capsule is comparable to the specific gravity of aramides.

The cement additive can be any cement additive imparting a beneficial interaction to the cement environment. Cement additives can include sealing reagents, anti-gas migration additives, accelerators, high-temperature retarders, fluid-loss additives, accelerators, superplasticizers, and combinations of the same. Sealing reagents can be any material capable of self-sealing fractured cement. Sealing reagents can include polymers, salts, rubber, water, latexes, epoxy, silicones, and combinations of the same. Sealing reagents can include a polymer with a T_(g), that is, a glass transition temperature where polymers become soft and flowable. In cases where the cement is compromised with micro-cracks, these sealing reagents self-seal the hardened cement to increase the workable lifetime of the well. In some embodiments, the cement additive is in a free-flowing powder form and is added, either wetted or not, to the dry mix when producing a slurry formulation. In some embodiments, the cement additive is water-soluble and can be dissolved in the dispersed solvent to form a dispersed phase.

The semi-permeable membrane can be an aramide polymer that is semi-permeable. The semi-permeable membrane can be a crosslinked aramide polymer. The aramide polymer can be formed through a polycondensation reaction. The polycondensation reaction can form other polymers suitable for the semi-permeable membrane, such as polyesters, polyurethanes, and polyureas. Examples of the aramide polymer that can form the semi-permeable membrane include polyamides, aramides, and combinations of the same. The semi-permeable membrane forms a shell encapsulating a core. The core contains the cement additive. The core can be a liquid core. Advantageously, aramides have high-temperature resistance and ballistic-rated strength. The semi-permeable membrane can be heat resistant up to temperatures of 400 deg. C. The semi-permeable membrane can maintain the integrity of the cement additive, resist chemical contamination of the cement additive, and keep the cement additive from degrading in the presence of the cement slurry until desired. The semi-permeable membrane can allow the cement additive to permeate from the core to outside the cement additive capsule. The cement additive can permeate through the semi-permeable membrane via osmosis, fluid displacement, or mechanical rupture. The semi-permeable membrane provides for a controlled release rate of the cement additive. The extent of crosslinking of the aramide polymer can determine the permeability of the semi-permeable membrane. The release rate can be controlled by adjusting the permeability of the semi-permeable membrane.

The aramide capsule can be formed through the method of interfacial polymerization. In the process of interfacial polymerization two immiscible fluids, such as a continuous phase and a dispersed phase, are blended together until the dispersed phase is dispersed as droplets in the continuous phase forming an emulsion. At least one phase contains a monomer and a crosslinker can be included in the other phase and the aramide polymer can form on the interface between the dispersed droplet and the continuous phase forming a shell around the droplet of the dispersed phase, such that the dispersed phase is captured within the shell. The shell formed through interfacial polymerization is the semi-permeable membrane.

The continuous phase can include a continuous solvent and a surfactant. In at least one embodiment, the continuous phase includes a crosslinker. In at least one embodiment, the crosslinker is added after the dispersed phase and the continuous phase have been blended. The continuous solvent can be any polar or non-polar solvent immiscible with water. Non-polar solvents suitable for use as the continuous solvent include oil, mineral oil, cyclohexane, chloroform, and combinations of the same. The crosslinker can be any acyl chloride monomer. Examples of crosslinkers include 1,3,5-benzenetricarbonyl trichloride, sebacoyl chloride, and combinations of the same. The surfactant can include sorbitan esters, polyethoxylated sorbitan esters, and combinations of the same.

The dispersed phase can include a dispersed solvent, a dispersed monomer, and the cement additive. The dispersed solvent can be any aqueous solvent that is immiscible with the continuous solvent. In at least one embodiment, the dispersed solvent can include water. The dispersed monomer can be any water-soluble diamine. The dispersed monomer can be any diamine monomer including a di-functional amino group. Examples of dispersed monomers include ethylenediamine, meta-phenylenediamine, para-phenylenediamine, hexamethylenediamine, and combinations of the same. The cement additives can be heterogeneous or solubilized. The cement additives can be blended into the dispersed phase. In at least one embodiment, the cement additives can be dissolved in the dispersed solvent to form the dispersed phase. In at least one embodiment, the dispersed phase can include a metal oxide.

The continuous phase solvent and the dispersed phase solvent can be selected such that the two fluids are immiscible with each other.

The continuous monomer and the dispersed monomer can be selected together in consideration of the properties of the aramide polymer that forms the semi-permeable membrane. The continuous monomer and the dispersed monomer can be selected to produce polyamides, aramides, polyesters, polyurethanes, polyureas, and combinations of the same. In at least one embodiment, the dispersed monomer can include ethylenediamine, meta-phenylenediamine, para-phenylenediamine, and combinations of the same. The crosslinker can include 1,3,5-benzenetricarbonyl trichloride. In at least one embodiment, the dispersed monomer can include hexamethylenediamine and the crosslinker can include sebacoyl chloride.

The amount of crosslinker added to the continuous phase can control permeability of the semi-permeable membrane. More than one continuous monomers or dispersed monomers can be used to control permeability of the semi-permeable membrane.

The continuous phase and the dispersed phase are blended together until the dispersed phase is dispersed as droplets in the continuous phase forming an emulsion. Depending on the volume of each phase a water-in-oil (w/o) emulsion or an oil-in-water (o/w) emulsion can be formed. The droplets can have different shapes including spheres, rods, fibers, and combinations of the same. The size of the droplets of the dispersed phase can be between 50 nanometers (nm) and 50 microns (μm), alternately between 100 nm and 1 μm, alternately between 1 μm and 10 μm, and alternately between 10 μm and 50 μm. The size and shape of the droplets of the dispersed phase in the continuous phase can be controlled by the shearing rate, the use of laminar flow, the dispersed solvent, the density of the dispersed solvent, the rate of blending of the continuous solvents and dispersed solvent, and viscosity of the dispersed phase. In at least one embodiment, laminar flow can be used form fibers. The size of the droplets can be optimized to impart a low rheological property to the cement slurry.

In at least one embodiment, the cement additive is insoluble in water but soluble in organic solvents. The continuous phase includes water as the continuous solvent and the dispersed phase includes the organic solvent as the dispersed solvent. Mixing the two phases may form an o/w emulsion for applications in oil-based drilling fluids.

In at least one embodiment, the crosslinker is present in the continuous phase when the two phases are blended together as a mixture and the aramide polymer begins to form as the emulsion is created. In at least one embodiment, the crosslinker is added to the mixture after the emulsion of dispersed droplets in the continuous phase has been developed.

The aramide polymer forms on the interface of the dispersed droplet and the continuous phase creating the aramide capsules. The polymerization reaction occurs at room temperature. The polymerization results in a covalently bonded crosslinked aramide polymer. The mixture is stirred to enhance homogeneity of the aramide polymer. In at least one embodiment, the mixture can be stirred for a period from about 24 hours to about 72 hours. In at least one embodiment, the aramide capsules can settle to the bottom of the reactor. In a next step, the aramide capsules are separated from the liquids remaining. The separation method used to separate the aramide capsules can be any process capable of separating a liquid and leaving behind dry capsules as a free-flowing powder. Separation methods can include decantation, filtration, centrifuging, rotary evaporation, vacuum drying, oven drying, and combinations of the same. In at least one embodiment, the separation method leaves a liquid at the core, creating a liquid filled capsule. In at least one embodiment, the separation method results in desiccation of the aramide capsule removing the liquid in the core. In at least one embodiment, the dry capsules can be washed to remove any residue of the continuous phase and then dried.

Additional reagents that can be added to the continuous phase and the dispersed phase include emulsifiers and viscosifiers. In at least one embodiment, the emulsifier added to the continuous phase is sorbitan trioleate. In at least one embodiment, the emulsifier added to the dispersed phase is polyethoxylated sorbitan ester.

The aramide capsule can be used to provide beneficial interaction with the cement environment. The aramide capsule is mixed with a cement slurry to form an additive-containing slurry. In at least one embodiment, the aramide capsule can be mixed with a cement slurry according to the API RP 10-B standard. The aramide capsule can be mixed with the cement slurry as a free-flowing dry powder, as liquid-filled capsules, or as part of a liquid emulsion. The aramide capsule can be used with any type of cement slurry. In at least one embodiment, the cement in the cement slurry is hydrophilic. In at least one embodiment, the cement slurry includes a class G Portland cement. In at least one embodiment, the cement additive is present in the cement slurry at a concentration of between 0.05% by weight of cement (bwoc) and 5% bwoc. In at least one embodiment, the aramide polymer of the semi-permeable membrane is present in the cement slurry at a concentration of at least 3% bwoc. In at least one embodiment, two or more aramide capsules can be added to the cement slurry, such that two or more different cement additives are carried into the cement slurry. The aramide capsule can be mixed within the cement slurry to distribute the aramide capsule through the cement slurry. The additive-containing slurry can be introduced to the formation according to any process for placing cement in a wellbore or formation. FIG. 1 is a photographic representation of the aramide capsules embedded in a cement slurry, as imaged by optical microscopy at ambient conditions.

The cement slurry sets into a hardened cement such that the aramide capsules are embedded in the hardened cement. In some embodiments, the hardened cement including the aramide capsules exhibits an unconfined compression strength ranging from about 2,500 psi to about 3,500 psi at about 350° F. for about 120 hours. In other embodiments, the hardened cement including the aramide capsules exhibits an unconfined compression strength ranging from about 2,800 psi to about 3,500 psi at about 350° F. for about 120 hours. Still in other embodiments, the hardened cement including the aramide capsules exhibits an unconfined compression strength ranging from about 3,000 psi to about 3,400 psi at about 350° F. for about 120 hours. For comparison, neat cement exhibits an unconfined compression strength in similar conditions ranging from about 3,000 psi to about 4,000 psi, from about 3,400 psi to about 3,700 psi, or from about 3,500 psi to about 3,600 psi. Also for comparison, latex-containing hardened cement exhibits an unconfined compression strength in similar conditions ranging from about 1,500 psi to about 2,500 psi, from about 1,800 psi to about 2,300 psi, or from about 1,900 psi to about 2,200 psi. In some embodiments, the hardened cement including the aramide capsules exhibits a confined compression strength ranging from about 5,000 psi to about 14,000 psi at room temperature. In other embodiments, the hardened cement including the aramide capsules exhibits a confined compression strength ranging from about 9,000 psi to about 12,000 psi at room temperature.

In at least one embodiment, the cement additive permeates from the core of the aramide capsule through the semi-permeable membrane to the cement environment surrounding the aramide capsule. In at least one embodiment, semi-permeable membrane of the aramide capsule can burst under the stress of the hardened cement. The cement additive then migrates through the cement environment. After the cement additive leaves the aramide capsules, the remaining aramide polymer of the semi-permeable membrane can impart strengthening properties to the matrix of the hardened cement.

In at least one embodiment, the beneficial interaction of the cement additive is to seal the cement. Sealing the cement makes the cement resistant to the influx of formation gases.

In at least one embodiment, the cement additive is tethered in the core of the aramide capsule via site-isolation using a linear polymer. The cement additive can be tethered to the semi-permeable membrane, tethered within the semi-permeable membrane, or tethered onto the semi-permeable membrane. In at least one embodiment, the cement additive can be site-isolated using linear polymers, such as polyethylene glycols (PEGs), polystyrenes, polyethylene imine, polyvinyl alcohols, polyvinylpyrrolidone, and combinations of the same. These linear polymers are typically water-soluble. The side chains of these linear polymers can be designed to contain the cement additive via chelation. Non-limiting examples of tethered cement additives include salts, accelerators, and metal catalysts. In other embodiments, these linear polymers can be cleaved such that the cleaved molecules can travel through the semi-permeable membrane. For example, linear polymers having carboxylic acid groups can be cleaved such that the cleaved molecule having the carboxylic acid group may serve as a cement retarder. In some embodiments, a viscosifier can be used to site-isolate the encapsulant.

Cement ductility refers to a measure of cement reliability where cement integrity is enhanced by making cement more elastic and ductile. Advantageously, the semi-permeable membrane of the aramide capsule improves cement ductility.

In at least one embodiment, the aramide capsule is in the absence of a molecular sieve.

Embodiments of the disclosure provide an aramide capsule in the absence of a cement additive. Without the cement additive, the aramide capsule has a hollow interior which can expand or contract depending on the osmotic properties of a surrounding fluid being in contact with the exterior of the aramide capsule. Fluids such as water can permeate through the semi-permeable membrane to the core when the aramide capsule is dry or surrounded with a hypotonic solution. On the other hand, fluids such as water can permeate from the core of a water-containing aramide capsule through the semi-permeable membrane to the surrounding environment when the water-containing aramide capsule is surrounded with a hypertonic solution. The aramide capsule is robust enough to survive multiple cycles of expansion and contraction without being ruptured.

In some embodiments, the aramid capsule formed as a result of interfacial polymerization has an average diameter ranging between about 10 μm and about 500 μm, alternately between about 50 μm and about 300 μm, or alternately between about 100 μm and about 200 μm. In some embodiments, the aramid capsule formed as a result of interfacial polymerization has an average wall thickness ranging between about 1 μm to about 10 μm, alternately between about 2 μm and about 7 μm, or alternately between about 3 μm and about 5 μm. In at least one embodiment, the aramid capsule has an average wall thickness of about 4 μm. The percent yield of the aramid capsule can range between about 5% and about 100%, alternately between about 30% and about 90%, or alternately between about 50% and about 80%. In at least one embodiment, the percent yield of the aramid capsule is about 76%. The density of the dried aramid capsule can range between about 1 gram per milliliter (g/ml) and about 1.7 g/ml, alternately between about 1.2 g/ml and 1.6 g/ml, or alternately between about 1.3 g/ml and 1.5 g/ml, indicative of an aromatic polyamide material. In at least one embodiment, the density of the dried aramid capsule is about 1.3 g/ml.

In at least one embodiment, the aramide capsule, as a free-flowing dry powder or as water-filled or salt-filled capsule, is mixed with cement to form a cement slurry. The aramide capsule can be used with any type of cement slurry. The cement slurry can have a water-to-cement mass ratio of between about 0.1 and about 5, alternately between about 0.1 and about 0.8, and alternately between about 0.45 and about 0.5. In at least one embodiment, the aramid polymer of the aramid capsules is present in the cement slurry at a concentration of between about 0.1% bwoc and about 5% bwoc, alternately between about 0.3% bwoc and about 4% bwoc, or alternately between about 0.5% bwoc and about 3% bwoc. In at least one embodiment the aramid polymer of the aramid capsules is present in the cement slurry at a concentration of about 3% bwoc. The aramide capsule can be mixed within the cement slurry to distribute the aramide capsule through the cement slurry. The cement slurry can be set to form a hardened cement such that the aramide capsules are embedded in the hardened cement.

In at least one embodiment, the aramide capsule is used as a cement additive to enhance the electrical conductivity of the cement. The chemical structure of the polymer used in the aramide capsule includes monomeric units including aromatic groups. Depending on the degree of aromaticity of the polymer, the aramide capsule can exhibit different electrical properties. For example, as the degree of aromaticity of the polymer increases, the aramide capsule can have a greater degree of electrical conductivity. As such, electrical conductivity of the aramide capsule-embedded hardened cement can be measured to determine whether the hardened cement is defective. Advantageously, the addition of the aramide capsule in the cement does not substantially negatively affect the structural properties of the cement.

In at least one embodiment, the aramide capsule can be used as a cement additive in a cemented wellbore. Electrical conductivity of the aramide capsule-embedded cemented wellbore can be measured to determine whether the cemented wellbore has any imperfections that may negatively affect the production of the wellbore.

In at least one embodiment, the aramide capsule can be used for the development of self-monitoring or self-sensing cements where certain deviations in resistivity/conductivity measurements (due to the physical, mechanical, and electrical properties of the aramide capsule) taken above ground can alert the operator to undertake remediation procedures to maintain cement sheath integrity. Advantageously, the scarce to zero hydrophobicity of the aramide capsules ensure uniform dispersion in the cement slurry, making it suitable for such monitoring applications.

In at least one embodiment, conductive properties of the aramide capsule-embedded cement allow the cement to be used for self-sealing microfractures, imperfections, and failures that may be present in the cement. The aramide capsule can include certain monomers as encapsulants that are designed to undergo polymerization reactions upon electron transfer (as known as living radical polymerization) such that block polymers can form in-situ. The monomers remain dormant within the aramide capsules until initiation of the polymerization reactions. For example, vinyl-based monomers (optionally with aldehyde or ketone based monomers) can be used as the encapsulant, where the free radical-based polymerization reaction can be initiated by photochemical or electrochemical means. The in situ-generated block polymer can form a downhole plug or seal, mitigate gas migration, block gas communication to the surface, seal microfractures, imperfections, and failures of downhole cement-based structures, increase the elasticity of the cement sheath, increase the integrity of the cement sheath, and expand the lifetime of the well.

In at least one embodiment, conductive properties of the aramide capsule-embedded cement allow the cement to be used in downhole cement structures such as casings. Due to the presence of the aramide capsules in the hardened cement, an operator can take resistivity measurements (either in-situ or at the surface) to determine whether lost circulation events are present.

In at least one embodiment, conductive properties of the aramide capsule-embedded cement allow the cement to be used as a heat source upon supplying power in order to melt snow or ice present in the cement. In a similar manner, the aramide capsule-embedded cement can be used as a heat sink that causes cyclic thermos-mechanical stresses to the cement. Without being bound by any theory, thermal energy is readily transferred between a given system and its surroundings. As such, thermal energy obtained from solar radiation (in the form of heat) or heated fluids (including gas and liquid) can be stored by the aramide capsules embedded in the cement to prevent the cement from heating and maintain constant temperature. The insoluble polymer shell of the aramide capsule is suitable for controlling cyclic changes in temperature as it does not dissolve or degrade, but rather remains intact. In addition, encapsulants such as waxes that can be placed within the hollow core of the aramide capsule can further enhance the heat sink feature. The intent is to keep the temperature of the cement constant with negligible or zero change, and to decrease stress strain and cement failure from such cyclic changes in temperature.

Advantageously, the electron-dense aramide capsules that are used in cement can be synthesized in a relatively inexpensive manner compared to other conductive materials used in cement, such as carbonic materials (for example, graphite, carbon nanotubes, and carbon black) and metallic materials.

EXAMPLES

The disclosure is illustrated by the following examples, which are presented for illustrative purposes only, and are not intended as limiting the scope of the invention which is define by the appended claims.

Example 1

In one non-limiting example, a polyamide was prepared by condensation of an aromatic tri-acid chloride with diamine at room temperature by interfacial polymerization. 1,3,5-benzenetricarboxylic acid chloride, trimesic acid trichloride, and trimesoyl chloride are examples of a tri-acid chloride. The diamine was dissolved in water or ethanol and added to a chloroform-cyclohexane solution containing an equal stoichiometric amount of the tri-acid chloride; an emulsifier was also added. Example diamines include ethylenediamine, 1,3-diaminobenzene, 1,4-diaminobenzene, 1,6-diaminohexane, 1,6-diaminohexane (mixed with sebacoyl chloride), and 1,4-phenylenediamine. In an embodiment, carboxylic acid is used in lieu of the tri-acid chloride.

Example 2

The reaction of 1,3,5-benzenetricarboxylic acid chloride with ethylenediamine and having a molar ratio of 2:3, which produces Polymer A is provided in Equation 1 below.

The molecular weight of Polymer A is 189 Daltons.

Example 3

The reaction of 1,3,5-benzenetricarboxylic acid chloride with 1,3-diaminobenzene and having a molar ratio of 2:3, which produces Polymer B, is provided in Equation 2 below.

The molecular weight of Polymer B is 265 Daltons.

Example 4

The reaction of 1,3,5-benzenetricarboxylic acid chloride with 1,4-diaminobenzene and having a molar ratio of 2:3, which produces Polymer C, is provided in Equation 3 below.

The molecular weight of Polymer C is 265 Daltons.

Example 5

The reaction of 1,3,5-benzenetricarboxylic acid chloride with 1,6-diaminohexane and having a molar ratio of 2:3, which produces Polymer D, is provided in Equation 4 below.

The molecular weight of Polymer D is 273 Daltons.

Example 6

The reaction of 1,3,5-benzenetricarboxylic acid chloride with 1,6-diaminohexane mixed with sebacoyl chloride and having a molar ratio of 1:3:1, which produces Polymer E, is provided in Equation 5 below.

The molecular weight of Polymer E is 555 Daltons.

Reactant ratios for forming Polymer A are not limited to that provided in Example 2 above. Alternative examples of producing Polymer A exist using amounts of 1,3,5-benzenetricarboxylic acid chloride in a range of from one to four and amounts of ethylenediamine in a range of two to six. Reactant ratios for forming Polymer B are not limited to that provided in Example 3 above. Alternative examples of producing Polymer B exist using amounts of 1,3,5-benzenetricarboxylic acid chloride in a range of from one to four and amounts of 1,3-diaminobenzene in a range of two to six. Reactant ratios for forming Polymer C are not limited to that provided in Example 4 above. Alternative examples of producing Polymer C exist using amounts of 1,3,5-benzenetricarboxylic acid chloride in a range of from one to four and amounts of 1,3-diaminobenzene in a range of two to six. Reactant ratios for forming Polymer D are not limited to that provided in Example 5 above. Alternative examples of producing Polymer D exist using amounts of 1,3,5-benzenetricarboxylic acid chloride in a range of from one to four and amounts of 1,6-diaminohexane in a range of two to six. Reactant ratios for forming Polymer E are not limited to that provided in Example 6 above. Alternative examples of producing Polymer E exist using amounts of 1,3,5-benzenetricarboxylic acid chloride in a range of from one to four, amounts of 1,6-diaminohexane in a range of two to six, and amounts of sebacoyl chloride in a range of from one to four.

Example 7

In a non-limiting example of use, an organic phase of 750 milliliters (ml) mixture of a 4:1 ratio of cyclohexane to CHCl₃ and two percent by volume of Span 85 is added to a 2 liter two-neck round bottom flask and stirred at 600 revolutions per minute (rpm) using a Caframo® BDC 2002 overhead stirrer. An aqueous solution of 200 ml of the diamines (1,6-diaminohexane, 1,4-diaminobenzene, 1,3-diaminobenzene, and ethylenediamine) is added to form an emulsion, which is stirred for 30 minutes. In preparation of interfacial polymerization, a solution of 26.5 grams of cross-linker 1,3,5-benzenetricarboxylic acid chloride dissolved in 200 ml of chloroform/CHCl₃ was added to the emulsion at a rate of 1 ml/minute, and the resulting solution was stirred for 1-2 hours. Advantageously, no heating was applied to the reactants during polymerization or during stirring. The resulting polymer was allowed to settle, and then decanted and washed with 500 ml of diethyl ether, 500 ml of tetrahydrofuran, and 500 ml of ethanol. The polymer was then transferred to a 250 ml round bottom flask, where it was concentrated by rotary evaporation and dried at temperature of 180 Fahrenheit (° F.) until a constant weight of free flowing powder was achieved. The bands of the infrared spectrum of 1,3-diaminobenzene and 1,4-diaminobenzene were measured after each condensation reaction.

In a non-limiting prophetic example a polymer is produced using the following constituents: 25.3 percent by weight of chloroform (solvent), 52.9 percent by weight of cyclohexane (continuous phase), 1.4 percent by weight of 1,6-diaminohexane, 2.4 percent by weight of 1,3,5-benzenetricarboxylic acid chloride, 0.1 percent by weight of surfactant, and 17.9 percent by weight of water (dispersed phase). The cyclohexane, chloroform, and surfactant are combined in a first mixing tank (not shown), and then seventy-five percent by volume of this solution is transferred to a reactor (not shown). In a second mixing tank (not shown), the 1-6 diaminohexane is dissolved in water and then added to the reactor to form an emulsion. In a third mixing tank (not shown) the 1,3,5-benzenetricarboxylic acid chloride is dissolved in the remaining twenty-five percent of the cyclohexane, chloroform, and surfactant mixture. The contents of the third mixing tank are added to the reactor at a constant rate to polymerize the emulsion; a byproduct of which is hydrochloric acid gas. The reactor contents are stirred for 24 hours for homogeneity. The polymer will settle in the reactor, and takes the form of a powder by removing the solvents and drying the polymer.

In an example, Polymer A is referred to as poly(ethylene trimesoylamide), Polymer B is referred to as poly-(meta-phenylene trimesoylamide), Polymer C is referred to as poly-(para-phenylene trimesoylamide), Polymer D is referred to as poly(hexamethylene trimesoylamide) (or crosslinked-“PA6T”-trimesoylamide), Polymer E is referred to as poly(hexamethylene-co-sebacoyl trimesoylamide) (crosslinked-“nylon610”-trimesoylamide), and Polymer E is referred to as poly-(para-phenylene trimesoylamide). Embodiments exist where Polymers A-E are formed in accordance with Example 1 above, and in an alternative, embodiments exist where Polymers A-E are formed in accordance with Example 7 above.

In one alternative, the polymer solution was stirred for 24 hours for homogeneity. A free-flowing powder was obtained by decanting, rotary evaporation, and filtration. Then, the polymer was further dried in an oven at 180° F. overnight or until a constant weight was achieved. To measure the heat resistance of the crosslinked aramide, a thermogravimetric analysis (TGA) technique was used to continuously measure the weight of a sample as a function of temperature (Q600 TGA, TA Instruments). High heat resistance is a characteristic of aramides.

Example 8

In one non-limiting example, a cement was prepared having a polymer. Example polymers for this example include Polymers A-E, a 1:1 blend of Polymers B and D, and combinations. A cement slurry was formed having four components: water, cement, 3% by weight of cement of the polymer applied, and anti-foamer. Optionally, the amount of polymer in the slurry can range from about 0.5% by weight of cement (“bwoc”) to about 5% bwoc. This range may be doubled and increased for more favorable results. Here, a 600-mL cement slurry with defoamer and polymer was prepared, where 24.2 grams of the polymer added to 806.9 grams of cement and 340.2 grams of water to make a 16.0 pound per gallon (ppg) cement. Any type of cement can be used in the cement slurry, including all Portland cements, any type of cement as classified by the American Society for Testing and Materials (ASTM), such as Type I, II, II, or V, any type of cement as classified by the American Petroleum Institute (API), such as Class A, C, G, or H, cements where latexes has been applied, white, pozzolana, and the like. Portland cements are described in API specification for “Materials and Testing for Well Cements”, API 10B-2 of the American Petroleum Institute. Embodiments exist having no additional chemical additives. Following API standards the slurry was blended at a mixing rate of 4,000 rpm for 14 seconds (s) and then increased to 12,000 rpm for 35 s. After mixing, the slurry was then poured into cube molds (2 cubic inches) or cylinder molds (2-inch diameter by 4-inch height). The samples were then placed into a curing chamber, where the cement remained for 72 hours at conditions of 180° F. and 3,000 pounds per square inch (psi). After curing, the cement was removed from the curing chamber and the sample surface prepared to measure its mechanical properties, such as compression strength.

Example 9

In a non-limiting example of forming a neat cement, 782.2 grams of Saudi G cement was mixed with 348.9 grams of water, which produced a slurry with a volume of 600 ml and a density of 15.8 ppg. The slurry was blended at 4,000 rpm for 15 s and blended at 12,000 rpm for 35 s, and poured into a brass mold. Inside the mold the cement was cured at 180° F. for 72 hours, and at a pressure of 3,000 psi. The ends of the samples were planed after curing so that surfaces of the samples were parallel. Examples of the cement are listed in Example 7 above.

Example 10

In a non-limiting example of use, a cement was prepared having 789.2 grams of Saudi G cement, 348.9 grams of water, and 23.7 grams (3% bwoc) of one of Polymers A-E, a 1:1 blend of Polymers B and D, and combinations. A 600-mL cement slurry as prepared having a density of 15.8 ppg. The slurry was blended at 4,000 rpm for 15 s, then blended at 12,000 rpm for 35 s, and poured into a brass mold. Inside the mold the cement was cured at 180° F. for 72 hours, and at a pressure of 3,000 psi. The ends of the samples were planed after curing so that surfaces of the samples were parallel. Examples of the cement are listed in Example 7 above.

Example 11

In a non-limiting example of use, a cement for prepared having 789.2 grams of Saudi G cement, 294.4 grams of water, 47.4 grams of a 50% latex solution (6% bwoc), and 7.1 grams of a stabilizer (15% by weight of the latex). Latex candidates include carboxylated latexes, and carboxylated styrene-butadiene latexes. The slurry was blended at 4,000 rpm for 15 s and blended at 12,000 rpm for 35 s, and poured into a brass mold. Inside the mold the cement was cured at 180° F. for 72 hours, and at a pressure of 3,000 psi. The ends of the samples were planed after curing so that surfaces of the samples were parallel. Examples of the cement are listed in Example 7 above.

Analysis of the polyamide synthesized from Equation 2 above demonstrated a material with a high temperature resistance up to 400° Celsius (° C.), and with weight loss of less than 4% at 195° C. In contrast, styrene-butadiene rubber (SBR) latexes have recommended maximum operating temperatures of 82° C. to 100° C. Shown in graphical form in FIG. 1 is an example of a graph 10 reflecting data obtained by analyzing the polyamide synthesized in Example 4. Graph 10 includes a line 12 that represents weight loss data and which was obtained by thermogravimetric analysis. Another line 14 is included with graph 10 and that represents data obtained using a differential scanning calorimetry. Values for weight percent are shown scaled along a left hand ordinate 16, values for heat flow (W/g) are scaled along a right hand ordinate 17, and an abscissa 18 provides a scale for temperature (° C.). Line 12, thus illustrates percent weight loss of the Equation 2 polyamide with respect to temperature, and shows that the polyamide percent weight loss remains substantially linear up to around 400° C., where it begins to decompose. SBR latexes on the other hand have a manufacturer's temperature recommendation of around 82° C. to about 100° C.

Additional increases in performance of the polymer cement described here included an increase in compression strength. For example, a percent (%) increase in mechanical property (x) is calculated as [1−(x for control cement)/(x for polymer cement)]*100. An increase in compression strength demonstrates the beneficial effects from crosslinked aramide application. Referring now to FIG. 2, shown is a graph 20 comparing the respective compressive strengths of neat, polyamide, and latex cements. A series of data points 22, 23, 24 on graph 20 respectively reflect measured compressive strengths over time of a latex based cement, a polyamide based cement (made with the 1,6-diaminohexane monomer), and a neat cement. Samples of the cements were loaded over time, thus values of load in pounds-force (“lbf”) are scaled along the ordinate 26 of graph 20, and values of time in seconds are scaled along the abscissa 28 of graph 20. A maximum compression strength of 25,667 lbf was measured for the latex based cements. Whereas the polyamide cement samples prepared in accordance with the present disclosure were tested and measured to have a maximum compression strength of over 34,167 lbf. The maximum compression strength of the neat cement approached 38,000 lbf.

FIGS. 3A-3C illustrate different cement blocks that underwent the compressive testing illustrated in FIG. 2. Shown in perspective view in FIG. 3A is an example of a sample 30 formed from cement made having an amount of polyamide, such as one or more of Polymers A-E discussed above. While the compressive testing formed a crack 32 in sample 30, the sample 30 otherwise remained substantially intact. FIG. 3B shows in a perspective view an example of a sample 34 made from a latex-cement, and FIG. 3C is a perspective view of a sample 36 made from neat cement and having no additives. Samples 34, 36 were each subjected to compressive loading, but instead of remaining substantially intact like the sample 30 of FIG. 3A, both samples 34, 36 crumbled. The latex-cement (or latex based cement) was made by adding about 3% by weight of latex to cement. Neat cement was made by mixing cement, water, and an anti-foaming agent.

FIG. 4 is a graph 38 of data obtained by measuring the compression strength of cement samples, while loading the cement samples at loading rates of 27 lbf/s, 267 lbf/s, and 865 lbf/s. The cement samples included samples having the polyamides made in accordance with Equations 1-4 above, a neat cement, and a latex based cement. Data points 40, 42, 44, 46, 48, and 50 are shown on the graph 38. The ordinate 52 of graph 38 is scaled to reflect compression strength in one thousand pounds per square inch and the abscissa 54 is scaled to the loading rate (lbf/s). Data point 40, represents the measured compression strength of the cement having the polyamide of Equation 1 above. Data point 42, represents the measured compression strength of the cement having the polyamide of Equation 2 above; data point 44, represents the measured compression strength of the cement having the polyamide of Equation 3 above; and data point 46, represents the measured compression strength of the cement having the polyamide of Equation 4 above. Data points 48, 50 reflect measured compression strength respectively of a neat cement and latex based cement. The neat cement and latex based cement that were tested were made in the same way as the neat cement and latex based cement tested and illustrated in FIGS. 3B and 3C.

As shown in FIG. 4, data point 40, which is a single data point, shows a loading rate of 287 lbf/s and a compression strength of around 4500 psi. Data points 42 reflect compression strengths of around 3500 psi at a loading rate of 27 lbf/s, and a compression strength of around 5600 for a loading rate of 287 lbf/s. Line L₄₂ is shown connecting the two data points 42. Data points 44 reflect compression strengths of around 3700 psi at a loading rate of 27 lbf/s, and a compression strength of around 5800 for a loading rate of 287 lbf/s. Line L₄₄ is shown connecting the two data points 44. Data point 46, which is also a single data point, shows a loading rate of 27 lbf/s with a corresponding compression strength of around 3700 psi. Data points 48 reflect compression strengths of around 4000 psi at a loading rate of 27 lbf/s, and a compression strength of around 6700 for a loading rate of 865 lbf/s. Line L₄₈ is shown connecting the two data points 48. Data points 50 reflect compression strengths of around 4500 psi at a loading rate of 27 lbf/s, and a compression strength of around 4800 for a loading rate of 287 lbf/s. Line L₅₀ is shown connecting the two data points 50. The cement samples having the polyamide of Equations 2 and 3 and having latex were not tested at the loading rate of 865 lbf/s, but how these samples would perform at that loading rate was estimated by extrapolating lines L₄₂, L₄₄, and L₅₀. The sample having the polyamide of Equation 1 was tested at a loading rate of 287 lb/s, and the sample having the polyamide of Equation 4 was tested at a loading rate of 27 lbf/s; as these produced single data points, no corresponding lines were formed. From FIG. 4 though it is clear that cement samples having polyamides have greater compression strengths at higher loading rates.

In a non-limiting example, static measurements and dynamic measurements were conducted on samples of neat cement, cement having latex, and on cement having some of the aramides of Examples 1-6 above. Static measurements were performed using a press (the NER Autolab 3000), which can obtain pressures up to 10,000 psi. The test equipment included an axial loading system, a confining pressure supply system, and data acquisition software. The samples measured were cylinders having a two inch diameter and a four inch length, and were jacketed and placed between steel end caps. Linear variable differential transformers (LVDTs) included with the press measured axial and radial deformation of the sample. The static measurements were taken at ambient temperature and a pressure of about 3,000 psi. The sample was placed in a triaxial cell and pressurized to a confining pressure of 30 MPa. Each cement sample was subjected to three axial load cycles. Plots of the loading cycles over time resemble triangular waveforms. In each loading series, an axially applied differential stress of 10 MPa was applied, and various peak axial stresses were applied. By applying uniaxial stress to the sample, its Young's modulus and Poisson's ratio were calculated based on strain measured by the LVDTs. Differences in failure mechanisms were identified for the different cement samples tested.

Dynamic measurements of the cement samples were performed with a Chandler MPRO instrument under confined conditions. The measurements were obtained at temperatures ranging from about 180° F. to about 350° F., and at a pressure of 3,000 psi. The samples remained in the instrument after curing, and measurements were taken as the cement was setting. Here, incremental increases in temperature after 20 hours measured cement response to thermal changes and the effects on different mechanical properties.

Tables 1A-1C below contains ranges of values of compression strength in psi, Young's modulus in psi, and Poisson's ratio for the samples of cement containing aramide, samples of neat cement, and samples of latex cement.

TABLE 1A (Aramide Cement) Compression Strength Young's modulus Poisson's (psi) (psi) Ratio Static 3000-5000 1.7 × 10⁶-2.2 × 10⁶ 0.23-0.33 Dynamic Variable 1.6 × 10⁶-1.9 × 10⁶ 0.35-0.37

TABLE 1B (Neat) Compression Strength Young's modulus Poisson's (psi) (psi) Ratio Static 5000-6500 2.0 × 10⁶ 0.2 Dynamic Variable 1.4 × 10⁶-1.9 × 10⁶ 0.35-0.36

TABLE 1C (Latex Cement) Compression Strength Young's modulus Poisson's (psi) (psi) Ratio Static 3000-5000 1.6 × 10⁶-1.9 × 10⁶ 0.25-0.35 Dynamic Variable 1.4 × 10⁶-1.9 × 10⁶ 0.35-0.36

Graphs 70, 72, 74, 76, 78 are shown respectively in FIGS. 5A-5E that reflect applied stresses and thermal cycle responses of cements having the following respective additives: latex, Polymer D, Polymer B, Polymer C, and a 1:1 combination of Polymers D and B (“the tested cements”). Plots 80, 82, 84, 86, 88 are respectively illustrated on the graphs 70, 72, 74, 76, 78 that depict measured values of strain resulting from stressing these cements. Ordinates 90, 92, 94, 96, 98 on the graphs 70, 72, 74, 76, 78 are scaled to illustrate values of stress in MPa, and abscissas 100, 102, 104, 106, 108 on the graphs 70, 72, 74, 76, 78 are scaled to represent values of strain in millistrain (mE). The graphs 70, 72, 74, 76, 78 were generated using data obtained from a series of laboratory tests that cyclically loaded the tested cements, while at the same time triaxially compressing the tested cements. The resulting stresses experienced by the tested cements were recorded and compared to the applied stresses to examine fatigue behavior of the tested cements. Each of the tested cements experienced some degree of hysteresis, that is, the stress-strain relationship of the tested cements followed different paths under subsequent loading cycles. This is best seen in FIG. 5A, where cement sample being tested contains latex. Here as illustrated by plot 80, the latex cement sample experienced a permanent strain of 26.7% after the three loading cycles. As shown in FIGS. 5B-5E, tested cements containing the polymers experienced deformations that were significantly lower than that of the latex cement of FIG. 5A, and which were unexpected. More specifically, the cement sample containing Polymer D experienced a 4.5% permanent strain (FIG. 5B), the cement sample containing Polymer B experienced an 11% permanent strain, the cement sample containing Polymer C experienced a 15.5% permanent strain, and the cement sample containing a blend of Polymers B and D experienced a 1.6% permanent strain. Not to be confined to theory, but it is believed that the intermolecular interaction between the polymeric structure and the cement surface is strong due to the reactive amide group.

Provided in FIG. 6A is a graph 110 containing plots 112, 114, 116, 118, 120, 122 that represent compression strength of various cements. Data obtained for plots 112, 114, 116, 118, 120, and 122 was respectively obtained by testing samples of neat cement, cement containing Polymer C, cement containing latex, cement containing Polymer B, cement containing Polymer D, and cement containing Polymer E. Units of the compression strength is in thousands of pounds per square inch (kpsi), and as reflected in FIG. 6A, the compression strength measurements were taken over a length of time and a range of temperatures. Values of compression strength are plotted along a left hand ordinate 124, values of temperature are plotted along a right hand ordinate 126, and values of time are plotted along abscissa 128. As illustrated in FIG. 6A, the temperature was 180° F. for 0 to about 70 hours, at 240° F. from about 70 hours to about 90 hours, at 300° F. from about 90 hours to about 115 hours, and 350° F. from about 115 hours to about 130 hours. The subsequent changes in temperature took place over a relatively short period of time and were generally instantaneous. As shown in the Example of FIG. 6A, compression strengths of every cement sample tested dropped at a substantial rate at each temperature increase. At temperatures equal to or greater than 240° F. the samples demonstrated a general reduction in magnitude over time, even when exposed to constant temperature. As illustrated by plot 114, the cement sample containing Polymer C possessed a compression strength having the largest magnitude at temperatures of 300° F. and greater, including neat cements and that having latex.

A graph 130 is shown in FIG. 6B having plots 132, 134, 136, 138, 140 that represent measured values of Young's modulus (×10⁶ psi) of samples respectively made up of cement having Polymer C, neat cement, cement having latex, cement having Polymer B, and cement having Polymer D. Values of Young's modulus are plotted along a left hand ordinate 142, values of temperature are plotted along a right hand ordinate 144, and values of time are plotted along abscissa 144. The values of temperature and respective durations used to generate the plots 132, 234, 136, 138, 140 of FIG. 6B were substantially the same as that used to generate the data for FIG. 6A. Similar to the results of FIG. 6A, the measured Young's modulus of the cement samples experienced a significant rate of decrease with each increase in temperature. Further illustrated in FIG. 6B is that the measured Young's modulus for the sample having Polymer C (plot 132) was greater than that of the samples having neat cement (plot 134) and cement with latex (plot 136). Further values obtained for Polymer C that are over the varying ranges of temperatures, include values of transit and shear velocity times. Transit velocity values ranged between 7 and 8 microseconds per inch for temperatures of 180° F. to 350° F., and which generally increased with increasing temperature. Shear velocity times ranged from about 15 to about 18 microseconds per inch for temperatures of 180° F. to 350° F. Shear velocity values also increased with increasing temperature.

In one non-limiting example of use, combining the reactants to form the polyamide generates an emulsion of a dispersed phase and a continuous phase; where the diamines are contained in the dispersed phase, and the triacid chloride is in the continuous phase. Vesicles are formed by interfacial polymerization along interfaces between the dispersed and continuous phase, and are made up at least in part by the polyamide. Due to additional processing, or compression within the cement, the vesicles are ruptured to form spent capsules. Thus in an embodiment, at least some of the polyamide in the cement is in the form of spent capsules, which are generally non-spherical, and range in shape from a planar configuration, to those with a cross section that approximates an ellipse. In an alternative, the polyamide spent capsules have distinct shapes that dynamically expand and contract, such as by osmosis. In an embodiment, the vesicles are emulsion templated, where the dispersed and continuous phase fluids yield the shape of the polyamide at the interface. Other possible shapes of the polyamide include hollowed fibers.

Referring now to FIG. 7, shown in a side partial sectional view is an example of a wellbore 148 intersecting a formation 150. Casing 152 lines the wellbore 148, and where cement 154 is disposed in an annular space between the casing 152 and wall of the wellbore 148. In an example, the cement 154 includes a polyamide, and can further include a polyamide made in accordance with the present disclosure, such as one or more of Polymers A-E and their combinations. A wellhead assembly 156 is shown mounted at an opening of the wellbore 148 and which contains pressure in the wellbore 148, as well as controlling flow from and into the wellbore 148. Production tubing 158 is shown deployed within the casing 152 and inside of which connate fluid produced from the formation 150 can be delivered to the wellhead assembly 156. An optional controller 160 is shown on surface and which is used to monitor downhole conditions in the wellbore 148, and that can convey signals downhole for operating production equipment (not shown), such as valves and packers.

In one example, crosslinking the aramide yields particles that are linear and particles that are three-dimensional. Thus crosslinking enhances the base polymer and forms a polymer network. Benefits of forming an aromatic compound include the advantages of rigidity and strength. Also, the alkane long chain of the 1,6-hexane diamine provides polymer flexibility. Another advantage of the polymer products described here include, the electron displacement between the amine, carbonyl and aromatic group, which yields an increase in binding between the polymer and the cement, and in turn enhances chemical interaction of the polymer to the cement. It has also been found to be advantageous to use different polymer moieties when forming the polyamide cement which increases ductility of cement and offers the potential for chemical interactions with cement and physical blocking by the polymer. In an example, physical blocking occurs when the polymers are insoluble they become particles embedded in the cement that serve as a physical barrier. These advantages provide a way to create a cement polymer with mechanical properties to prolong the lifespan of wellbore cement sheaths, thereby preventing cement casing annulus pressure problems

Example 12

A number of samples of aramide capsules were formed according to the methods described. The continuous solvent was a 4:1 cyclohexane-chloroform blend. The surfactant was a 1.5% by volume sorbitan trioleate (Span-85®, Sigma-Aldrich®, St. Louis, Mo.). The continuous phase included the continuous solvent and the surfactant. The crosslinker was 1,3,5-benzenetricarbonyl trichloride. The dispersed solvent was water. The dispersed monomer was 1,6-diaminohexane. The cement additive was the dispersant sulfonated acetone-formaldehyde condensate (SAFC). The dispersed phase included the dispersed solvent, the dispersed monomer, and the cement additive. SAFC has a red color, and so acted as a dye or a signaling molecule in Example 12. The SAFC allowed measurements to be taken of the release rate from the capsules.

The aramide capsules were prepared at room temperature. 25 ml of the continuous phase was added to 3 ml of the dispersed phase. The mixture was stirred for 15 minutes forming a w/o emulsion. After 15 minutes of stirring the crosslinker was added to the mixture in an amount in milliMolars (mM) according to Table 2. For each sample, the crosslinker was added at a rate of about 1.5 ml per minute. Stirring continued while the crosslinker was being added. Stirring maintained the w/o emulsion.

TABLE 2 Sample Amount of Crosslinker (mM) A 23 B 46 C 77 D 154

After 20 minutes, polymerization was stopped by filtering the solid aramide capsules. The aramide capsules were washed with 500 ml of a sodium bicarbonate buffer solution (1% weight per volume (w/v), pH˜8.3). The washed aramide capsules were vacuum dried.

The aramide capsules were placed onto a microscope slide and placed under an optical microscope with a mounted digital camera and a power source. FIG. 8 shows an optical micrograph image 800 of the aramide capsules 810 containing the SAFC encapsulant.

Example 13

Polymerization of each sample formed in Example 12 was stopped at predetermined intervals by filtering the solid aramide capsules. Each aramide capsule sample was subjected to a multi-wash process. Each sample was washed with diethyl ether then washed with 500 ml of a sodium bicarbonate buffer solution (1% w/v, pH˜8.3).

UV/Vis spectrophotometry was employed to obtain absorbance curves of SAFC for each sample. Each sample was introduced into a UV/Vis spectrophotometer (λ_(max)=420 nm, from Hach, Loveland, Colo.) to measure absorbance. Calibration was performed by taking 1 ml calibration samples of each sample. After settling for a few hours, the calibration samples were filtered by using a 0.45 μm nylon syringe filter. The filtered calibration samples were introduced into the UV/Vis spectrophotometer to measure absorbance of free SAFC (that is, SAFC that is not contained in the aramide capsules) in solution. The absorbance spectrum of each sample was calibrated with the absorbance spectrum of the corresponding free SAFC calibration sample.

The results were shown in FIG. 9. FIG. 9 is a graphical representation 900 showing UV/Vis absorbance of the encapsulant released from the aramide capsules over time. The horizontal axis represents time in minutes. The vertical axis represents UV/Vis absorbance in arbitrary units. Square points 910 and the corresponding regression curve 912 represent absorbance of Sample A in Example 12 having 23 mM of crosslinker. Circular points 920 and the corresponding regression curve 922 represent absorbance of Sample B in Example 12 having 46 mM of crosslinker. Triangular points 930 and the corresponding regression curve 932 represent absorbance of Sample C in Example 12 having 77 mM of crosslinker. Reverse-triangular points 940 and the corresponding regression curve 942 represent absorbance of Sample D in Example 12 having 154 mM of crosslinker.

FIG. 9 shows that the amount of dye that diffused into the supernatant was inversely dependent on the amount of the crosslinker. FIG. 9 also shows that the permeability, and as a result the release rate of the encapsulant, can be controlled by the amount of crosslinker added to the mixture. An increase in the concentration of the crosslinker resulted in a decrease in membrane permeability.

Example 14

An aramide capsule was formed according to the methods described. The continuous solvent was a 4:1 cyclohexane-chloroform blend. The surfactant was a 1.5% by volume sorbitan trioleate (Span-85®, Sigma-Aldrich®, St. Louis, Mo.). The continuous phase included the continuous solvent and the surfactant. The crosslinker was 1,3,5-benzenetricarbonyl trichloride. The dispersed solvent was water. The dispersed monomer was 1,6-diaminohexane. The encapsulant was polyethylenimine (PEI). The dispersed phase included the dispersed solvent, the dispersed monomer, and the encapsulant.

The aramide capsules were prepared at room temperature. 25 ml of the continuous phase was added to 3 ml of the dispersed phase. The mixture was stirred for 15 minutes forming a w/o emulsion. After 15 minutes of stirring 40 ml of the crosslinker (0.02 M solution) was added to the mixture. For each sample, the crosslinker was added at a rate of about 1.5 ml per minute. Stirring continued while the crosslinker was being added. Stirring maintained the w/o emulsion.

After 30 minutes, polymerization was stopped by filtering the solid aramide capsules. The aramide capsules were washed with 500 ml of a sodium bicarbonate buffer solution (1% w/v, pH˜8.3). The washed aramide capsules were vacuum dried in an oven.

The aramide capsules were placed onto a microscope slide and placed under an optical microscope with a mounted digital camera and a power source. FIG. 10 shows an optical micrograph image 1000 of the aramide capsule 1010 containing the PEI encapsulant 1020.

Example 15

A number of samples of aramide capsules were formed according to the methods described. The continuous solvent was a 4:1 cyclohexane-chloroform blend. The surfactant was a 1.5% by volume sorbitan trioleate (Span-85®, Sigma-Aldrich®, St. Louis, Mo.). The continuous phase included the continuous solvent and the surfactant. The crosslinker was 1,3,5-benzenetricarbonyl trichloride. The dispersed solvent was water. The dispersed monomer was 1,6-diaminohexane. The cement additive was the dispersant SAFC condensate. The dispersed phase included the dispersed solvent, the dispersed monomer, and the cement additive. SAFC has a red color, and so acted as a dye or a signaling molecule. The SAFC allowed measurements to be taken of the release rate from the aramide capsules.

The aramide capsules were prepared at room temperature. 25 ml of the continuous phase was added to 3 ml of the dispersed phase. The dispersed phase included 130 mM of the dispersed monomer. The dispersed phase included 0.5% bwoc of the SAFC encapsulant. The mixture was stirred for 15 minutes forming a w/o emulsion. After 15 minutes of stirring, the crosslinker in an amount in mM according to Table 3 was added to the mixture at a rate of about 1.5 ml per minute. Stirring continued while the crosslinker was being added. Stirring maintained the w/o emulsion.

TABLE 3 Amount of Amount of Amount of SAFC Crosslinker Dispersed Encapsulant Sample (mM) Monomer (mM) (% bwoc) E 16 130 0.5 F 50 130 0.5 G 65 130 0.5 H 82 130 0.5

Polymerization was stopped at a predetermined interval of about 24 hours where the w/o emulsion was filtered to produce the solid aramide capsules. The aramide capsules were washed with 500 ml of a borate buffer solution. The washed aramide capsules were vacuum dried producing a free flowing powder.

A cement slurry was formed having water, cement, and 3% bwoc of the aramide capsules. Any type of cement can be used in the cement slurry, including all Portland cements, any type of cement as classified by the American Society for Testing and Materials (ASTM), such as Type I, II, III, or V, and any type of cement as classified by the American Petroleum Institute (API), such as Class A, C, G, or H. Portland cements are described in API specification for “Materials and Testing for Well Cements,” API 10B-2 of the API. Following API standards the slurry was blended at 4,000 rpm for 15 s and then increased to 12,000 rpm for 35 s. The slurry was placed in a rheometer (Anton Paar GmbH, Graz, Austria) to measure changes in viscosity over time.

The results were shown in FIG. 11. FIG. 11 is a graphical representation 1100 showing viscosity of the cement slurry having the encapsulant within the aramide capsule samples of varying monomer concentration. The horizontal axis represents concentration of the crosslinker in mM. The vertical axis represents viscosity of the cement slurry in centipoise (cP). Square points 1110 and the corresponding lines 1112 represent viscosities of cement slurries having Samples E-G collected at 0 minutes of mixing the slurry. Circular points 1120 and the corresponding lines 1122 represent viscosities of cement slurries having Samples E-G collected at 10 minutes of mixing the slurry. Triangular points 1130 and the corresponding lines 1132 represent viscosities of cement slurries having Samples E-G collected at 20 minutes of mixing the slurry. Reverse-triangular points 1140 and the corresponding lines 1142 represent viscosities of cement slurries having Samples E-G collected at 30 minutes of mixing the slurry.

FIG. 11 shows that the viscosity of the cement slurry was dependent on the amount of the crosslinker. FIG. 11 also shows that the permeability, and as a result the release rate of the encapsulant, can be controlled by the amount of the crosslinker added to the mixture. An increase in the concentration of the crosslinker resulted in a decrease in membrane permeability.

Example 16

A number of samples of aramide capsules were formed according to the methods described. The continuous solvent was a 4:1 cyclohexane-chloroform blend. The surfactant was a 1.5% by volume sorbitan trioleate (Span-85®, Sigma-Aldrich®, St. Louis, Mo.). The continuous phase included the continuous solvent and the surfactant. The crosslinker was 1,3,5-benzenetricarbonyl trichloride. The dispersed solvent was water. The dispersed monomer was 1,6-diaminohexane. The cement additive was the dispersant SAFC. The dispersed phase included the dispersed solvent, the dispersed monomer, and the cement additive. SAFC has a red color, and so acted as a dye or a signaling molecule. The SAFC allowed measurements to be taken of the release rate from the aramide capsules.

The aramide capsules were prepared at room temperature. The dispersed phase included the dispersed monomer in an amount in mM according to Table 4. The dispersed phase included 0.5% bwoc of the SAFC encapsulant. The mixture was stirred for 15 minutes forming a w/o emulsion. After 15 minutes of stirring, the crosslinker in an amount in mM according to Table 4 was added to the mixture at a rate of about 1.5 ml per minute. Stirring continued while the crosslinker was being added. Stirring maintained the w/o emulsion.

TABLE 4 Amount of Amount of Amount of SAFC Crosslinker Dispersed Encapsulant Sample (mM) Monomer (mM) (% bwoc) I (free dispersant, no 0 0 0.5 capsules in cement) J 20 130 0.5 K 50 130 0.5 L 80 130 0.5

Polymerization was stopped at a predetermined interval of about 24 hours where the w/o emulsion was filtered to produce the solid aramide capsules. The aramide capsules were washed with 500 ml of a diethyl ether and borate buffer solution. The washed aramide capsules were vacuum dried.

A cement slurry was formed having water, cement, and 3% bwoc of the aramide capsules. In addition to the cement slurries having aramide capsules, a neat cement slurry was also formed having water and cement. Any type of cement can be used in the cement slurry, including all Portland cements, any type of cement as classified by ASTM, such as Type I, II, III, or V, and any type of cement as classified by API, such as Class A, C, G, or H. Portland cements are described in API specification for “Materials and Testing for Well Cements,” API 10B-2 of the API. Following API standards the slurry was blended at 4,000 rpm for 15 s and then increased to 12,000 rpm for 35 s. The slurry was placed in a rheometer (Anton Paar GmbH, Graz, Austria) to measure changes in viscosity over time.

The results are shown in FIG. 12. FIG. 12 is a graphical representation 1200 showing viscosity of the cement slurry having aramide capsule samples over time. The horizontal axis represents time in minutes. The vertical axis represents viscosity of the cement slurry in cP. Empty circular points 1210 and the corresponding lines 1212 represent viscosities of the cement slurry having Sample I over time. Square points 1220 and the corresponding lines 1222 represent viscosities of the cement slurry having Sample J over time. Triangular points 1230 and the corresponding lines 1232 represent viscosities of the cement slurry having Sample K over time. Reverse-triangular points 1240 and the corresponding lines 1242 represent viscosities of the cement slurry having Sample L over time. Filled circular points 1250 and the corresponding lines 1252 represent viscosities of the neat cement slurry over time.

FIG. 12 shows that the viscosity of the cement slurry was dependent on the amount of the crosslinker. FIG. 12 also shows that the permeability, and as a result the release rate of the encapsulant, can be controlled by the amount of the crossliner added to the mixture. An increase in the concentration of the crosslinker resulted in a decrease in membrane permeability.

Example 17

A capsule-based cement having aramide capsules was prepared. Example aramide capsules include aramide capsules formed in Examples 12-16. A cement slurry was formed having water, cement, and 3% bwoc of the aramide capsules. Any type of cement can be used in the cement slurry, including all Portland cements, any type of cement as classified by ASTM, such as Type I, II, III, or V, and any type of cement as classified by API, such as Class A, C, G, or H. Portland cements are described in API specification for “Materials and Testing for Well Cements,” API 10B-2 of the API. Following API standards the slurry was blended at 4,000 rpm for 15 s and then increased to 12,000 rpm for 35 s.

A neat cement was prepared. A cement slurry was formed having water and cement. Any type of cement can be used in the cement slurry, including all Portland cements, any type of cement as classified by ASTM, such as Type I, II, III, or V, and any type of cement as classified by API, such as Class A, C, G, or H. Portland cements are described in API specification for “Materials and Testing for Well Cements,” API 10B-2 of the API. The slurry was blended at 4,000 rpm for 15 s, and blended at 12,000 rpm for 35 s.

A latex-based cement was prepared. A cement slurry was formed having water, cement, 6% bwoc of a 50% latex solution, and 15% by weight of the latex solution a stabilizer. Any type of cement can be used in the cement slurry, including all Portland cements, any type of cement as classified by ASTM, such as Type I, II, III, or V, and any type of cement as classified by API, such as Class A, C, G, or H. Portland cements are described in API specification for “Materials and Testing for Well Cements,” API 10B-2 of the API. Example latexes include carboxylated latexes and carboxylated styrene-butadiene latexes. The slurry was blended at 1,000 rpm for 35 s.

After mixing, each slurry was poured into a sample holder of an ultrasonic cement analyzer (UCA, from Chandler Engineering, Broken Arrow, Okla.) for measuring confined compression strength. The UCA is suitable for curing cement slurries and conducting in situ testing of cements at wellbore conditions. Each slurry was then placed into a curing chamber to start the measurement, where the cement remained for a period of about 72 hours to about 120 hours at about 350° F. and about 3,000 psi.

The results are shown in FIG. 13. FIG. 13 shows a graphical representation 1300 of unconfined compression strengths of cement samples formed in Example 17. Graphical representations 1310, 1320, 1330 correspond to the unconfined compression strengths of the neat cement, the aramide capsule-based cement, and the latex-based cement, respectively. The vertical axis represents the unconfined compression strength in psi. The horizontal axis represents time in hours. As shown in FIG. 13, the neat cement exhibits an unconfined compression strength ranging from about 3,500 psi to about 3,600 psi, at about 350° F. for about 120 hours. The capsule-based cement exhibits an unconfined compression strength ranging from about 3,000 psi to about 3,400 psi, at about 350° F. for about 120 hours. The latex-based cement exhibits an unconfined compression strength ranging from about 1,900 psi to about 2,200 psi, at about 350° F. for about 120 hours.

FIG. 13 shows that cement strength retrogression occurs significantly for the latex-based cements compared to neat cement at wellbore conditions. On the other hand, cement strength retrogression does not significantly occur for the capsule-based cement, showing that the aramide capsules and the cement additives within the capsules provide structural integrity to the cement.

Example 18

A sample of aramide capsules were formed according to the method described. The continuous solvent was a 4:1 cyclohexane-chloroform blend. The surfactant was sorbitan trioleate (Span-85®, Sigma-Aldrich®, St. Louis, Mo.). The continuous phase included the continuous solvent and 2% by volume of the surfactant. The crosslinker was 1,3,5-benzenetricarbonyl trichloride. The dispersed solvent was water. The dispersed monomer was PEI. The dispersed phase included the dispersed solvent and the dispersed monomer.

The aramide capsules were prepared at room temperature. About 16 grams of the dispersed monomer was added to 200 ml of water to produce the dispersed phase. 26.5 grams of the crosslinker was added to 200 ml of the continuous solvent to produce a crosslinker solution. The dispersed phase was combined with 750 ml of the continuous phase. The mixture was vigorously hand-shaken for about three minutes to form an emulsion and was subject to centrifugation for 15 seconds at 3,000 rpm. One skilled in the relevant art would recognize that the shape of the aramide capsules can vary depending on the flow rate of the dispersed phase (during its addition to the continuous phase) and the shearing rate of the continuous phase (for example, by the overhead stir mixer). The aramide capsules can have various shapes including spherical droplets, elongated shapes (such as oval or tear drops), fiber shapes, fiber bundles, vesicles attached to other shapes, and detached vesicles with one or more tails.

Polymerized aramide capsules were filtered. The aramide capsules were washed with 500 ml of a sodium bicarbonate buffer solution (1% weight per volume (w/v), pH˜8.3). The aramide capsules were filtered once more and were spread over a flat surface to dry in a vacuum oven at about 82° C. overnight, until no change in weight was observed. Clumps of the aramide capsules were broken up using a 35-mesh screen to form a free flowing powder. The yield ranged between about 38% and about 85%. In at least one embodiment, the yield was about 60%.

Example 19

A sample of aramide capsules were formed according to the method described. The continuous solvent was a 4:1 cyclohexane-chloroform blend. The surfactant was sorbitan trioleate (Span-85®, Sigma-Aldrich®, St. Louis, Mo.). The continuous phase included the continuous solvent and 2% by volume of the surfactant. The crosslinker was 1,3,5-benzenetricarbonyl trichloride. The dispersed solvent was water. The dispersed monomer was 1,3-diaminobenzene (MDA). The dispersed phase included the dispersed solvent and the dispersed monomer.

The aramide capsules were prepared at room temperature. About 16 grams of the dispersed monomer was added to 200 ml of water to produce the dispersed phase. 26.5 grams of the crosslinker was added to 200 ml of the continuous solvent to produce a crosslinker solution. The dispersed phase was combined with 750 ml of the continuous phase. The mixture was stirred for about 30 minutes at about 600 rpm (without turbulent mixing) using a Caframo BDC2002 overhead stirrer forming a w/o emulsion. After 30 minutes of stirring the crosslinker solution was added to the mixture at a rate of about 1 ml per minute. Stirring continued while the crosslinker solution was being added. Stirring continued for an additional 24-50 hours, maintaining the w/o emulsion. One skilled in the relevant art would recognize that the shape of the aramide capsules can vary depending on the flow rate of the dispersed phase (during its addition to the continuous phase) and the shearing rate of the continuous phase (for example, by the overhead stir mixer). The aramide capsules can have various shapes including spherical droplets, elongated shapes (such as oval or tear drops), fiber shapes, fiber bundles, vesicles attached to other shapes, and detached vesicles with one or more tails.

Stirring was stopped and the solid aramide capsules were filtered. The aramide capsules were washed with 500 ml of a sodium bicarbonate buffer solution (1% weight per volume (w/v), pH˜8.3). The aramide capsules were filtered once more and were spread over a flat surface to dry in a vacuum oven at about 82° C. overnight, until no change in weight was observed. Clumps of the aramide capsules were broken up using a 35-mesh screen to form a free flowing powder. The yield was about 76.3%. FIG. 14 shows a graphical representation of a time-dependent increase in yield of the MDA-based aramide capsules having data points at 2, 8, 15, and 24 hours of stirring.

Example 20

Each of the dried aramide capsules obtained in Examples 18 and 19 was placed onto a microscope slide and placed under an optical microscope with a mounted CCD camera (AxioCam, Carl Zeiss, Oberkochen, Germany) and a power source. All images were acquired and processed using the Axio Vision (Zen Pro, Carl Zeiss, Oberkochen, Germany) software.

FIG. 15A is a schematic representation of the chemical structure of the PEI-based aramide capsules obtained in Example 18. FIG. 15B shows a dark field optical micrograph image of the PEI-based aramide capsules obtained in Example 18, showing fluorescence between 420 and 470 nm upon exposure to excitation wavelengths between 335 and 383 nm. FIG. 15C shows a light field optical micrograph image of the PEI-based aramide capsules obtained in Example 18. The PEI-based aramide capsules had a diameter ranging between 500 and 1,200 microns. FIG. 15D shows a superimposed fluorescence micrograph image of the PEI-based aramide capsule obtained in Example 18 using a compound microscope (Axio Imager M2m, Carl Zeiss, Oberkochen, Germany) with Nomarski objective lens. One of the fluorescence micrograph image used in the superimposed fluorescence micrograph image was obtained by using an external xenon lamp and a HE DsRed filter (Carl Zeiss, Oberkochen, Germany) having excitation wavelengths between 538 and 562 nm and emission wavelengths between 570 and 640 nm. The other of the fluorescence micrograph image used in the superimposed fluorescence micrograph image was obtained by using an external xenon lamp and a DAPI filter (Carl Zeiss, Oberkochen, Germany) having excitation wavelengths between 335 and 383 nm and emission wavelengths between 420 and 470 nm.

FIG. 16A is a schematic representation of the chemical structure of the MDA-based aramide capsules obtained in Example 19. FIG. 16B shows a dark field optical micrograph image of the MDA-based aramide capsules obtained in Example 19, showing fluorescence between 520 and 550 nm upon exposure to excitation wavelengths between 490 and 510 nm. FIG. 16C shows a light field optical micrograph image of the MDA-based aramide capsules obtained in Example 19. The MDA-based aramide capsules had a diameter ranging between 10 and 500 microns.

As can be seen by comparing FIGS. 15A and 16A, the MDA-based aramide capsules have a greater degree of aromaticity (per unit monomer) than that of the PEI-based aramide capsules due to the abundancy of aromatic rings and increased π-electron density, which is evidenced by comparing the optical properties of the two types of aramide capsules. Without being bound by any theory, the degree of aromaticity depends on the type of crosslinker used. In some embodiments, the chloride pendent group of the 1,3,5-benzenetricarboxylic acid chloride can be substituted with any suitable electron donating group having non-bonding electron pairs (such as —NH₂, —OH, —O⁻, —NHR, —OR, —NHC(═O)R, and -Ph) to enhance the luminescence properties of the vesicle, where an n→π electron resonance can take part in donating electron density. In some embodiments, the benzene can be substituted with any suitable π-electron dense moiety (such as aromatics other than benzene) to enhance the luminescence properties of the aramide capsules, where π→π stacking interactions can take part in donating electron density. Without being bound by any theory, the degree of aromaticity of the aramide capsules has a positive correlation with the degree of robustness of the aramide capsules, where structural rigidity at the molecular level, in turn, facilitates fluorescence due to conjugation. In comparison, alkyl groups seldom contribute to fluorescence. In some embodiments, encapsulants such as water-soluble organic or inorganic fluorescence enhancers (such as certain biological compounds, vitamins, gold nanoparticles, or cadmium sulfide) can further enhance fluorescence properties of the aramide capsules.

As can be seen by comparing FIGS. 15C and 16C, the degree of opacity (and robustness) increases as the reaction time to produce the aramide capsules increases, which can be observed by light field microscopy. The MDA-based aramid capsules (having a 24 hour reaction time) tend to be more opaque than the PEI-based aramide capsules (having a 3 minute reaction time).

As can be seen by comparing FIGS. 15B and 16B, the fluorescence intensity increases as the reaction time to produce the aramide capsules increases, which can be observed by dark field microscopy. For example, greater fluorescence intensity is observed for a 24 hour reaction time for the MDA-based aramide capsules than a 3 minute reaction time for the PEI-based aramide capsules. In addition, the fluorescence intensity increases as the degree of aromaticity increases. Without being bound by any theory, the MDA-based aramide capsules tend to have a greater degree of bulk electron conjugation than the PEI-based aramide capsules. However, as shown in Example 18, the PEI-based aramide capsules can be prepared by simply hand-shaking the mixture including the dispersed phase and the continuous phase for about three minutes while exhibiting sufficient fluorescence properties, as evidenced in FIG. 15D. That is, without being bound by any theory, the reaction time has a positive correlation with the robustness of the aramide capsules, where the intensity of the fluorescence may vary, but qualitatively the aramide capsules generally fluoresce. Such relative ease of preparation makes the PEI-based aramide capsules suitable for luminescence-based applications such as sensors, promoters, signaling, and markers.

Example 21

Cement samples were prepared by mixing 300 grams of Class G cement and 135 grams of water to form cement slurries with varying quantities (1, 2, and 3% bwoc) of the aramide capsules (in the free flowing powder form) obtained from Example 19. The cement slurry was subsequently hardened. A neat cement sample was prepared using the same procedure but in the absence of the aramide capsules. A defective cement sample was prepared using the same procedure with 3% bwoc of the aramide capsules where the hardened cement included physical defects.

Electrical resistivity of each of the cement sample and the neat cement sample was measured using a 4-point Wenner probe (Resipod, Proceq, Schwerzenbach, Switzerland). The distance between adjacent electrodes of the Wenner probe was about 12 cm. The Wenner probe was operated at an AC frequency of about 40 Hz. Two sets of four measurements spaced 90 degrees per sample were averaged to determine the electrical resistivity of each sample. The electrical resistivity measurements were taken compliant to standard test methods including AASHTO TP 95-14 and ASTM C1202. The results are shown in Table 5 and FIG. 17.

TABLE 5 Sample Electrical Resistivity (in kΩ-cm) Neat cement 19.4 ± 0.24 Aramide-based cement (3% bwoc) 14.1 ± 0.22 Defective aramide-based cement 382.2

FIG. 17 shows a graphical representation of electrical resistivity of each of the cement sample and the neat cement sample. As the aramide capsule content of the cement sample increases, the electrical resistivity decreases. The cement sample having 3% bwoc of the aramide capsules showed a 27% reduction in electrical resistivity than the neat cement sample, indicative of an increase in electrical conductivity. The defective cement sample showed electrical resistivity at least one order of magnitude greater than any of the non-defective cement samples or the neat cement sample. The results show that the aramide-based cement can be used for monitoring the integrity of the cement by measuring electrical resistivity (or conductivity).

Further modifications and alternative embodiments of various aspects of the disclosure will be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the embodiments described in the disclosure. It is to be understood that the forms shown and described in the disclosure are to be taken as examples of embodiments. Elements and materials may be substituted for those illustrated and described in the disclosure, parts and processes may be reversed or omitted, and certain features may be utilized independently, all as would be apparent to one skilled in the art after having the benefit of this description. Changes may be made in the elements described in the disclosure without departing from the spirit and scope of the disclosure as described in the following claims. Headings used described in the disclosure are for organizational purposes only and are not meant to be used to limit the scope of the description. 

What is claimed is:
 1. A method for monitoring structural integrity of a hardened cement, the method comprising the steps of: mixing an aramide capsule, a cement, and a water to form a cement slurry, where the aramide capsule is formed by the steps of: mixing a continuous solvent and a surfactant to produce a continuous phase; mixing a dispersed solvent and a dispersed monomer to produce a dispersed phase, where the dispersed solvent and the continuous solvent are immiscible; mixing the continuous phase and the dispersed phase to form a mixture having an emulsion such that the dispersed phase is dispersed as droplets in the continuous phase, where an interface defines the droplets of the dispersed phase dispersed in the continuous phase; adding a crosslinker to the mixture; allowing an aramide polymer to form on the interface of the droplets, such that the aramide polymer forms a semi-permeable membrane around a core, where the core contains the dispersed phase, such that the semi-permeable membrane around the core forms the aramide capsule; allowing the aramide capsule to settle from the mixture; separating the aramide capsule from the mixture using a separation method; and drying the aramide capsule such that the core is hollow, where the aramide capsule exists as a free flowing powder; allowing the cement slurry to set to form the hardened cement, where the aramide capsule is embedded in the hardened cement; and detecting imperfections of the hardened cement by measuring electrical resistivity of the hardened cement.
 2. The method of claim 1, where the cement slurry has a water-to-cement mass ratio ranging between 0.1 and 0.8.
 3. The method of claim 1, where the aramide polymer of the aramide capsule is present in the cement slurry at a concentration ranging between 0.5% and 5% by weight of the cement.
 4. The method of claim 1, where the aramide capsule has a diameter ranging between 500 and 1,200 microns.
 5. The method of claim 1, where the aramide capsule has a diameter ranging between 10 and 500 microns.
 6. The method of claim 1, where the aramide capsule has a wall thickness ranging between 3 and 5 microns.
 7. The method of claim 1, where the dispersed solvent is selected from the group consisting of water, ethanol, methanol, and combinations of the same.
 8. The method of claim 1, where the dispersed monomer is selected from the group consisting of polyethylenimine, 1,4-diaminobenzene, 1,3-diaminobenzene, 1,6-diaminohexane, and combinations of the same.
 9. The method of claim 1, where the continuous solvent is selected from the group consisting of cyclohexane, chloroform, and combinations of the same.
 10. The method of claim 1, where the crosslinker is 1,3,5-benzenetricarbonyl trichloride.
 11. A method for monitoring structural integrity of a cemented wellbore, the method comprising the steps of: mixing an aramide capsule, a cement, and a water to form a cement slurry, where the aramide capsule is formed by the steps of: mixing a continuous solvent and a surfactant to produce a continuous phase; mixing a dispersed solvent and a dispersed monomer to produce a dispersed phase, where the dispersed solvent and the continuous solvent are immiscible; mixing the continuous phase and the dispersed phase to form a mixture having an emulsion such that the dispersed phase is dispersed as droplets in the continuous phase, where an interface defines the droplets of the dispersed phase dispersed in the continuous phase; adding a crosslinker to the mixture; allowing an aramide polymer to form on the interface of the droplets, such that the aramide polymer forms a semi-permeable membrane around a core, where the core contains the dispersed phase, such that the semi-permeable membrane around the core forms the aramide capsule; allowing the aramide capsule to settle from the mixture; separating the aramide capsule from the mixture using a separation method; and drying the aramide capsule such that the core is hollow, where the aramide capsule exists as a free flowing powder; injecting the cement slurry into a drilled wellbore; allowing the cement slurry to set to form the cemented wellbore, where the aramide capsule is embedded in the cemented wellbore; and detecting imperfections of the cemented wellbore by measuring electrical conductivity of the cemented wellbore.
 12. The method of claim 11, where the cement slurry has a water-to-cement mass ratio ranging between 0.1 and 0.8.
 13. The method of claim 11, where the aramide polymer of the aramide capsule is present in the cement slurry at a concentration ranging between 0.5% and 5% by weight of the cement.
 14. The method of claim 11, where the aramide capsule has a diameter ranging between 500 and 1,200 microns.
 15. The method of claim 11, where the aramide capsule has a diameter ranging between 10 and 500 microns.
 16. The method of claim 11, where the aramide capsule has a wall thickness ranging between 3 and 5 microns.
 17. The method of claim 11, where the dispersed solvent is selected from the group consisting of water, ethanol, methanol, and combinations of the same.
 18. The method of claim 11, where the dispersed monomer is selected from the group consisting of polyethylenimine, 1,4-diaminobenzene, 1,3-diaminobenzene, 1,6-diaminohexane, and combinations of the same.
 19. The method of claim 11, where the continuous solvent is selected from the group consisting of cyclohexane, chloroform, and combinations of the same.
 20. The method of claim 11, where the crosslinker is 1,3,5-benzenetricarbonyl trichloride. 